[BUG] admin无法启动

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Current Behavior

使用nacos作为服务发现时,服务shenyu-examples-http注册了,然后这个服务下线了,重启admin会报错:

shenyu discovery start watcher need you has this key shenyu-examples-http in Discovery
at org.apache.shenyu.admin.discovery.DefaultDiscoveryProcessor.createProxySelector(DefaultDiscoveryProcessor.java:56)
at org.apache.shenyu.admin.service.impl.DiscoveryServiceImpl.lambda$syncData$1(DiscoveryServiceImpl.java:265)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
at org.apache.shenyu.admin.service.impl.DiscoveryServiceImpl.syncData(DiscoveryServiceImpl.java:249)
at org.apache.shenyu.admin.service.impl.DiscoveryServiceImpl.syncData(DiscoveryServiceImpl.java:276)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
at java.base/java.lang.reflect.Method.invoke(Method.java:580)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:354)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:196)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:768)
at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:123)
at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:392)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:119)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:184)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:768)
at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:720)
at org.apache.shenyu.admin.service.impl.DiscoveryServiceImpl$$SpringCGLIB$$0.syncData()
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
at java.base/java.lang.reflect.Method.invoke(Method.java:580)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:354)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:196)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:768)
at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:123)
at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:392)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:119)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:184)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:768)
at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:720)
at org.apache.shenyu.admin.service.impl.DiscoveryServiceImpl$$SpringCGLIB$$1.syncData()
at org.apache.shenyu.admin.service.impl.SyncDataServiceImpl.syncAll(SyncDataServiceImpl.java:133)
at org.apache.shenyu.admin.listener.AbstractDataChangedInit.run(AbstractDataChangedInit.java:39)
at org.springframework.boot.SpringApplication.lambda$callRunner$5(SpringApplication.java:790)
at org.springframework.util.function.ThrowingConsumer$1.acceptWithException(ThrowingConsumer.java:83)
at org.springframework.util.function.ThrowingConsumer.accept(ThrowingConsumer.java:60)
at org.springframework.util.function.ThrowingConsumer$1.accept(ThrowingConsumer.java:88)
at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:798)
at org.springframework.boot.SpringApplication.callRunner(SpringApplication.java:789)
at org.springframework.boot.SpringApplication.lambda$callRunners$3(SpringApplication.java:774)
at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:184)
at java.base/java.util.stream.SortedOps$SizedRefSortingSink.end(SortedOps.java:357)
at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:510)
at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499)
at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:151)
at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:174)
at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:596)
at org.springframework.boot.SpringApplication.callRunners(SpringApplication.java:774)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:342)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1363)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1352)
at org.apache.shenyu.admin.ShenyuAdminBootstrap.main(ShenyuAdminBootstrap.java:36)

看代码是admin在初始化的时候会去nacos获取服务的信息,服务不存在直接抛出了异常:

### Expected Behavior

admin正常启动

### Steps To Reproduce

_No response_

### Environment

```markdown
ShenYu version(s):
```

### Debug logs

_No response_

### Anything else?

_No response_

Start with org.apache.shenyu.admin.discovery.DefaultDiscoveryProcessor.java:56 and DiscoveryServiceImpl.java:249, 265, and 276, following the initialization path shown in the stack trace. Reproduce with Nacos after shenyu-examples-http has gone offline, then verify that the admin starts normally without failing on the missing discovery key.

Written by the indexing model from the issue text.