Improve exception when cluster is not available

[berndruecker]

This exception is not 100% self-explanatory:

2023-03-23 16:08:31.466  WARN 28732 --- [ault-executor-0] io.camunda.zeebe.client.job.poller       : Failed to activate jobs for worker noopJobWorker#noop and job type noop

io.grpc.StatusRuntimeException: CANCELLED
	at io.grpc.Status.asRuntimeException(Status.java:539)
	at io.grpc.stub.ClientCalls$StreamObserverToCallListenerAdapter.onClose(ClientCalls.java:487)
	at io.grpc.internal.ClientCallImpl.closeObserver(ClientCallImpl.java:576)
	at io.grpc.internal.ClientCallImpl.access$300(ClientCallImpl.java:70)
	at io.grpc.internal.ClientCallImpl$ClientStreamListenerImpl$1StreamClosed.runInternal(ClientCallImpl.java:757)
	at io.grpc.internal.ClientCallImpl$ClientStreamListenerImpl$1StreamClosed.runInContext(ClientCallImpl.java:736)
	at io.grpc.internal.ContextRunnable.run(ContextRunnable.java:37)
	at io.grpc.internal.SerializingExecutor.run(SerializingExecutor.java:133)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
	at java.base/java.lang.Thread.run(Thread.java:833)
Caused by: java.io.IOException: Failed while requesting access token with status code 404 and message Not Found.
	at io.camunda.zeebe.client.impl.oauth.OAuthCredentialsProvider.fetchCredentials(OAuthCredentialsProvider.java:183)
	at io.camunda.zeebe.client.impl.oauth.OAuthCredentialsProvider.refreshCredentials(OAuthCredentialsProvider.java:132)
	at io.camunda.zeebe.client.impl.oauth.OAuthCredentialsProvider.loadCredentials(OAuthCredentialsProvider.java:121)
	at io.camunda.zeebe.client.impl.oauth.OAuthCredentialsProvider.applyCredentials(OAuthCredentialsProvider.java:79)
	at io.camunda.zeebe.client.impl.ZeebeCallCredentials.lambda$applyRequestMetadata$0(ZeebeCallCredentials.java:48)
	... 3 common frames omitted