Add support to add reactive hook when initializing MCP server

[raducoravu]

I create and initialize a McpSyncClient.

McpSyncClient client = McpClient.sync(transport)
          .requestTimeout(timeout)
          .loggingConsumer(this)
          .capabilities(ClientCapabilities.builder()
              .roots(true)      // Enable filesystem roots support
              .sampling()       // Enable LLM sampling support
              .build())
          .build();
client.initialize();

I get this error logged in the console:

java.lang.RuntimeException: Failed to start process with command: [npx, -y, @modelcontextprotocol/server-brave-search]
	at io.modelcontextprotocol.client.transport.StdioClientTransport.lambda$connect$1(StdioClientTransport.java:124)
	at reactor.core.publisher.MonoRunnable.call(MonoRunnable.java:73)
	at reactor.core.publisher.MonoRunnable.call(MonoRunnable.java:32)
	at reactor.core.publisher.FluxSubscribeOnCallable$CallableSubscribeOnSubscription.run(FluxSubscribeOnCallable.java:228)
	at reactor.core.scheduler.SchedulerTask.call(SchedulerTask.java:68)
	at reactor.core.scheduler.SchedulerTask.call(SchedulerTask.java:28)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:317)
	at

but I do not seem to have a way to add a hook to the reactor.core.publisher.Operators.onErrorDropped(Throwable, Context) context object from the MCP code so that I can for example present the error to the end user.
Now I have to use the static reactor.core.publisher.Hooks.onErrorDropped(Consumer<? super Throwable>) which is not very elevant.