Allow edge workload run after client node restart & lost internet connection

### Proposal

Edge workload maybe have unstable internet connection or power source. For unstable connection we can use [disconnect](https://developer.hashicorp.com/nomad/docs/job-specification/disconnect) block to handle this condition. however when client node restart because unstable power and at same time internet connection also lost, existing nomad allocation cannot be started because the node has not successfully registered/reconnected to the nomad server.

Example:
1. Submit job

```
job "edge-app" {

region = "global"

group "edge-app" {

disconnect {
lost_after = "6h"
replace = false
reconcile = "best_score"
}

task "edge-app" {
driver = "raw_exec"
config {
command = "local/my-app"
}
artifact {
source = "https://url-to-binary-app/my-app"
}
}
}
}
```

2. Client node restart becasue lost power source & at same time internet connection also lost
3. `disconnect` block working

Client node mark mark as disconnect rather than down

```
ID Node Pool DC Name Class Drain Eligibility Status
6723722e default edge ip-172-31-5-240 false eligible disconnected
```

Allocation mark as unknown

```
Allocations
ID Node ID Task Group Version Desired Status Created Modified
edb17146 6723722e edge-app 17 run unknown 6m13s ago 3m34s ago
```

4. Client node try to connect to server after lost power source & internet

```
Dec 08 15:15:19 ip-172-31-5-240 nomad[529]: 2024-12-08T15:15:19.369Z [INFO] client.alloc_runner.task_runner: Task event: alloc_id=edb17146-2c06-49f6-d8db-27408e9e6a69 task=edge-app type=Received msg="Task received by client" failed=false
Dec 08 15:15:19 ip-172-31-5-240 nomad[529]: 2024-12-08T15:15:19.369Z [ERROR] client.driver_mgr.raw_exec: failed to reattach to executor: driver=raw_exec error="error creating rpc client for executor plugin: Reattachment process not found" task_id=edb17146-2c06-49f6-d8db-27408e9e6a69/edge-app/891c72c5
Dec 08 15:15:19 ip-172-31-5-240 nomad[529]: 2024-12-08T15:15:19.369Z [ERROR] client.alloc_runner.task_runner: error recovering task; cleaning up: alloc_id=edb17146-2c06-49f6-d8db-27408e9e6a69 task=edge-app error="failed to reattach to executor: error creating rpc client for executor plugin: Reattachment process not found" task_id=edb17146-2c06-49f6-d8db-27408e9e6a69/edge-app/891c72c5
Dec 08 15:15:19 ip-172-31-5-240 systemd[1]: Started nomad.service - Nomad.
Dec 08 15:15:19 ip-172-31-5-240 nomad[529]: 2024-12-08T15:15:19.369Z [INFO] client.alloc_runner.task_runner: Task event: alloc_id=edb17146-2c06-49f6-d8db-27408e9e6a69 task=edge-app type="Failed Restoring Task" msg="failed to restore task; will not run until server is contacted" failed=false
Dec 08 15:15:19 ip-172-31-5-240 nomad[529]: 2024-12-08T15:15:19.373Z [INFO] client: started client: node_id=6723722e-0ec8-b6ca-99b3-9f86a562bbb7
Dec 08 15:15:19 ip-172-31-5-240 nomad[529]: 2024-12-08T15:15:19.381Z [INFO] client.alloc_runner.task_runner: task failed to restore; waiting to contact server before restarting: alloc_id=edb17146-2c06-49f6-d8db-27408e9e6a69 task=edge-app
Dec 08 15:15:29 ip-172-31-5-240 nomad[529]: 2024-12-08T15:15:29.348Z [ERROR] client.rpc: error performing RPC to server: error="rpc error: failed to get conn: dial tcp 123.x.x.x:4647: i/o timeout" rpc=Node.Register server=123.x.x.x:4647
Dec 08 15:15:29 ip-172-31-5-240 nomad[529]: 2024-12-08T15:15:29.349Z [ERROR] client.rpc: error performing RPC to server which is not safe to automatically retry: error="rpc error: failed to get conn: dial tcp 123.x.x.x:4647: i/o timeout" rpc=Node.Register server=123.x.x.x:4647
Dec 08 15:15:29 ip-172-31-5-240 nomad[529]: 2024-12-08T15:15:29.349Z [ERROR] client: error registering: error="rpc error: failed to get conn: dial tcp 123.x.x.x:4647: i/o timeout"
Dec 08 15:15:29 ip-172-31-5-240 nomad[529]: 2024-12-08T15:15:29.349Z [ERROR] client.rpc: error performing RPC to server: error="rpc error: failed to get conn: rpc error: lead thread didn't get connection" rpc=Node.GetClientAllocs server=123.x.x.x:4647
Dec 08 15:15:29 ip-172-31-5-240 nomad[529]: 2024-12-08T15:15:29.349Z [ERROR] client.rpc: error performing RPC to server which is not safe to automatically retry: error="rpc error: failed to get conn: rpc error: lead thread didn't get connection" rpc=Node.GetClientAllocs server=123.x.x.x:4647
Dec 08 15:15:29 ip-172-31-5-240 nomad[529]: 2024-12-08T15:15:29.349Z [ERROR] client: error querying node allocations: error="rpc error: failed to get conn: rpc error: lead thread didn't get connection"
```

5. At this time existing allocation is not running

I think if nomad is able to run the previous allocation from the above conditions it would be a good thing.

### Use-cases

Edge workload with unstable internet connection & power source.

### Attempted Solutions

Start by tracing client allocation recovery after the node restart, focusing on the disconnect behavior and the raw_exec reattachment failure shown in the logs. Review the Node.Register and Node.GetClientAllocs paths to understand what happens while the client cannot reach the server. Done means an existing disconnect-enabled allocation can recover and run after a client restart with a simultaneous network outage.

Written by the indexing model from the issue text.