Transient failure causes end-to-end failure in SQL execution

## Bug Report

A transient failure (service unavailable) in PD finally causes the failure of end-to-end SQL execution. The failure is not handled in pd nor tidb.
When the following RPC fails with unavailable:
```
runtime.goexit:1223;net/http.(*conn).serve:2092;net/http.serverHandler.ServeHTTP:3210;go.etcd.io/etcd/server/v3/embed.(*accessController).ServeHTTP:458;net/http.(*ServeMux).ServeHTTP:2747;github.com/urfave/negroni.(*Negroni).ServeHTTP:96;github.com/urfave/negroni.middleware.ServeHTTP:38;github.com/urfave/negroni.(*Recovery).ServeHTTP:193;github.com/urfave/negroni.middleware.ServeHTTP:38;github.com/urfave/negroni.HandlerFunc.ServeHTTP:29;github.com/urfave/negroni.(*Negroni).UseHandler.Wrap.func1:46;github.com/gorilla/mux.(*Router).ServeHTTP:210;github.com/gorilla/mux.(*Router).ServeHTTP:210;github.com/urfave/negroni.(*Negroni).ServeHTTP:96;github.com/urfave/negroni.middleware.ServeHTTP:38;github.com/tikv/pd/pkg/utils/apiutil/serverapi.(*runtimeServiceValidator).ServeHTTP:48;github.com/urfave/negroni.middleware.ServeHTTP:38;github.com/tikv/pd/pkg/utils/apiutil/serverapi.(*redirector).ServeHTTP:187;github.com/urfave/negroni.middleware.ServeHTTP:38;github.com/urfave/negroni.HandlerFunc.ServeHTTP:29;github.com/tikv/pd/server/api.NewHandler.Wrap.func21:46;github.com/gorilla/mux.(*Router).ServeHTTP:210;net/http.HandlerFunc.ServeHTTP:2220;github.com/tikv/pd/server/api.clusterMiddleware.middleware-fm.clusterMiddleware.middleware.func1:101;github.com/urfave/negroni.(*Negroni).ServeHTTP:96;github.com/urfave/negroni.middleware.ServeHTTP:38;github.com/tikv/pd/server/api.(*requestInfoMiddleware).ServeHTTP:78;github.com/urfave/negroni.middleware.ServeHTTP:38;github.com/tikv/pd/server/api.(*auditMiddleware).ServeHTTP:152;github.com/urfave/negroni.middleware.ServeHTTP:38;github.com/tikv/pd/server/api.(*rateLimitMiddleware).ServeHTTP:184;github.com/urfave/negroni.middleware.ServeHTTP:38;github.com/urfave/negroni.HandlerFunc.ServeHTTP:29;github.com/tikv/pd/server/api.(*serviceMiddlewareBuilder).createHandler.WrapFunc.func1:56;github.com/tikv/pd/server/api.(*regionLabelHandler).PatchRegionLabelRules:71;github.com/tikv/pd/pkg/schedule/labeler.(*RegionLabeler).Patch:302;github.com/tikv/pd/pkg/storage/endpoint.RunBatchOpInTxn:94;github.com/tikv/pd/pkg/storage/kv.(*etcdKVBase).RunInTxn:215;github.com/tikv/pd/pkg/storage/kv.(*etcdTxn).commit:287;github.com/tikv/pd/pkg/storage/kv.(*SlowLogTxn).Commit:171;go.etcd.io/etcd/client/v3.(*txn).Commit:145;go.etcd.io/etcd/client/v3.(*retryKVClient).Txn:117;go.etcd.io/etcd/api/v3/etcdserverpb.(*kVClient).Txn:6487
```

And try to delete database
```
mysql> drop database access_path_selection;
ERROR 8243 (HY000): "rpc error: code = Unavailable desc = transient error"
```

The RPC from tidb to pd is as below
```
[2025/05/15 06:43:36.622 +00:00] [INFO] [audit.go:128] ["audit log"] [service-info="{ServiceLabel:PatchRegionLabelRules, Method:HTTP/1.1/PATCH:/pd/api/v1/config/region-label/rules, CallerID:tidb-info-syncer, IP:10.244.1.79, Port:60058, StartTime:2025-05-15 06:43:36 +0000 UTC, URLParam:{}, BodyParam:{\"sets\":[],\"deletes\":[\"schema/access_path_selection/access_path_selection\"]}}"]
```

### What did you do?

Inject a transient error between pd and tikv(?) and try to delete the database.

### What did you expect to see?

PD handles this bug with a retry.

### What did you see instead?

PD raises this error to tidb and tidb does not handle it as well.
The log of tidb is shown below:
```
[2025/05/15 06:43:36.470 +00:00] [INFO] [session.go:4111] ["CRUCIAL OPERATION"] [conn=3078628316] [schemaVersion=23107] [cur_db=] [sql="drop database access_path_selection"] [user=root@%]
[2025/05/15 06:43:36.552 +00:00] [INFO] [executor.go:6613] ["DDL job submitted"] [category=ddl] [job="ID:22826, Type:drop schema, State:queueing, SchemaState:public, SchemaID:22819, TableID:0, RowCount:0, ArgLen:1, start time: 2025-05-15 06:43:36.444 +0000 UTC, Err:, ErrCount:0, SnapshotVersion:0, Version: v2"] [query="drop database access_path_selection"]
[2025/05/15 06:43:36.570 +00:00] [INFO] [job_submitter.go:139] ["add DDL jobs"] [category=ddl] ["batch count"=1] [jobs="ID:22826, Type:drop schema, State:queueing, SchemaState:public, SchemaID:22819, TableID:0, RowCount:0, ArgLen:1, start time: 2025-05-15 06:43:36.444 +0000 UTC, Err:, ErrCount:0, SnapshotVersion:0, Version: v2; "] [table=true] [fast_create=true]
[2025/05/15 06:43:36.578 +00:00] [INFO] [job_worker.go:784] ["run DDL job"] [category=ddl] [jobID=22826] [conn=3078628316] [job="ID:22826, Type:drop schema, State:queueing, SchemaState:public, SchemaID:22819, TableID:0, RowCount:0, ArgLen:0, start time: 2025-05-15 06:43:36.444 +0000 UTC, Err:, ErrCount:0, SnapshotVersion:0, Version: v2"]
[2025/05/15 06:43:36.656 +00:00] [WARN] [info.go:523] ["response not 200"] [method=PATCH] [host=basic-pd-0.basic-pd-peer.default.svc:2379] [url=/pd/api/v1/config/region-label/rules] ["http status"=500]
[2025/05/15 06:43:36.659 +00:00] [INFO] [job_worker.go:717] ["DDL job is cancelled normally"] [category=ddl] [jobID=22826] [conn=3078628316] [error="[domain:8243]\"rpc error: code = Unavailable desc = outbound unavailable injected by RPCTest\"\n"]
[2025/05/15 06:43:36.661 +00:00] [INFO] [job_worker.go:390] ["finish DDL job"] [category=ddl] [jobID=22826] [conn=3078628316] [job="ID:22826, Type:drop schema, State:cancelled, SchemaState:public, SchemaID:22819, TableID:0, RowCount:0, ArgLen:1, start time: 2025-05-15 06:43:36.444 +0000 UTC, Err:[domain:8243]\"rpc error: code = Unavailable desc = outbound unavailable injected by RPCTest\"\n, ErrCount:1, SnapshotVersion:0, Version: v2"]
[2025/05/15 06:43:36.697 +00:00] [INFO] [executor.go:6738] ["DDL job is failed"] [category=ddl] [jobID=22826]
[2025/05/15 06:43:36.698 +00:00] [INFO] [tidb.go:278] ["rollbackTxn called due to ddl/autocommit failure"]
[2025/05/15 06:43:36.699 +00:00] [WARN] [session.go:2162] ["run statement failed"] [conn=3078628316] [session_alias=] [schemaVersion=23107] [error="[domain:8243]\"rpc error: code = Unavailable desc = outbound unavailable injected by RPCTest\"\n"] [session="{\n \"currDBName\": \"\",\n \"id\": 3078628316,\n \"status\": 2,\n \"strictMode\": true,\n \"user\": {\n \"Username\": \"root\",\n \"Hostname\": \"127.0.0.1\",\n \"CurrentUser\": false,\n \"AuthUsername\": \"root\",\n \"AuthHostname\": \"%\",\n \"AuthPlugin\": \"mysql_native_password\"\n }\n}"]
[2025/05/15 06:43:36.704 +00:00] [INFO] [conn.go:1184] ["command dispatched failed"] [conn=3078628316] [session_alias=] [connInfo="id:3078628316, addr:127.0.0.1:59450 status:10, collation:utf8mb4_general_ci, user:root"] [command=Query] [status="inTxn:0, autocommit:1"] [sql="drop database access_path_selection"] [txn_mode=PESSIMISTIC] [timestamp=458041961072295938] [err="[domain:8243]\"rpc error: code = Unavailable desc = outbound unavailable injected by RPCTest\"\n\ngithub.com/pingcap/errors.AddStack\n\t/root/go/pkg/mod/github.com/pingcap/errors@v0.11.5-0.20240318064555-6bd07397691f/errors.go:178\ngithub.com/pingcap/errors.Trace\n\t/root/go/pkg/mod/github.com/pingcap/errors@v0.11.5-0.20240318064555-6bd07397691f/juju_adaptor.go:15\ngithub.com/pingcap/tidb/pkg/ddl.(*executor).DoDDLJobWrapper\n\t/workspace/source/tidb/pkg/ddl/executor.go:6739\ngithub.com/pingcap/tidb/pkg/ddl.(*executor).doDDLJob2\n\t/workspace/source/tidb/pkg/ddl/executor.go:6555\ngithub.com/pingcap/tidb/pkg/ddl.(*executor).DropSchema\n\t/workspace/source/tidb/pkg/ddl/executor.go:772\ngithub.com/pingcap/tidb/pkg/executor.(*DDLExec).executeDropDatabase\n\t/workspace/source/tidb/pkg/executor/ddl.go:338\ngithub.com/pingcap/tidb/pkg/executor.(*DDLExec).Next\n\t/workspace/source/tidb/pkg/executor/ddl.go:169\ngithub.com/pingcap/tidb/pkg/executor/internal/exec.Next\n\t/workspace/source/tidb/pkg/executor/internal/exec/executor.go:456\ngithub.com/pingcap/tidb/pkg/executor.(*ExecStmt).next\n\t/workspace/source/tidb/pkg/executor/adapter.go:1266\ngithub.com/pingcap/tidb/pkg/executor.(*ExecStmt).handleNoDelayExecutor\n\t/workspace/source/tidb/pkg/executor/adapter.go:1015\ngithub.com/pingcap/tidb/pkg/executor.(*ExecStmt).handleNoDelay\n\t/workspace/source/tidb/pkg/executor/adapter.go:848\ngithub.com/pingcap/tidb/pkg/executor.(*ExecStmt).Exec\n\t/workspace/source/tidb/pkg/executor/adapter.go:611\ngithub.com/pingcap/tidb/pkg/session.runStmt\n\t/workspace/source/tidb/pkg/session/session.go:2288\ngithub.com/pingcap/tidb/pkg/session.(*session).ExecuteStmt\n\t/workspace/source/tidb/pkg/session/session.go:2150\ngithub.com/pingcap/tidb/pkg/server.(*TiDBContext).ExecuteStmt\n\t/workspace/source/tidb/pkg/server/driver_tidb.go:291\ngithub.com/pingcap/tidb/pkg/server.(*clientConn).handleStmt\n\t/workspace/source/tidb/pkg/server/conn.go:2026\ngithub.com/pingcap/tidb/pkg/server.(*clientConn).handleQuery\n\t/workspace/source/tidb/pkg/server/conn.go:1779\ngithub.com/pingcap/tidb/pkg/server.(*clientConn).dispatch\n\t/workspace/source/tidb/pkg/server/conn.go:1378\ngithub.com/pingcap/tidb/pkg/server.(*clientConn).Run\n\t/workspace/source/tidb/pkg/server/conn.go:1147\ngithub.com/pingcap/tidb/pkg/server.(*Server).onConn\n\t/workspace/source/tidb/pkg/server/server.go:741\nruntime.goexit\n\t/usr/local/go/src/runtime/asm_arm64.s:1223"]
```

### What version of PD are you using (`pd-server -V`)?

v8.5.0