Update java exception rules to support reactor/webflux formatted exception

[sethrylan]

Steps to reproduce

1. Configure fluent-plugin-detect-exceptions

    <match raw.kubernetes.**>
      @id exceptions
      @type detect_exceptions
      remove_tag_prefix raw
      message message
      stream stream
      multiline_flush_interval 5
      max_bytes 500000
      max_lines 1000
    </match>

2. Create an exception on a reactive thread. These exceptions follow the format

org.springframework.web.reactive.function.client.WebClientRequestException: finishConnect(..) failed: Connection refused: localhost:8080; nested exception is io.netty.channel.AbstractChannel$AnnotatedConnectException: finishConnect(..) failed: Connection refused: localhost:8080
	at org.springframework.web.reactive.function.client.ExchangeFunctions$DefaultExchangeFunction.lambda$wrapException$9(ExchangeFunctions.java:141)
	Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException:
Error has been observed at the following site(s):
	|_ checkpoint ⇢ Request to GET localhost:8080
Stack trace:
		at org.springframework.web.reactive.function.client.ExchangeFunctions$DefaultExchangeFunction.lambda$wrapException$9(ExchangeFunctions.java:141)
		at reactor.core.publisher.MonoErrorSupplied.subscribe(MonoErrorSupplied.java:70)
		at reactor.core.publisher.Mono.subscribe(Mono.java:4150)
		at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onError(FluxOnErrorResume.java:103)
		at org.springframework.cloud.sleuth.instrument.reactor.ScopePassingSpanSubscriber.onError(ScopePassingSpanSubscriber.java:95)
		at reactor.core.publisher.FluxPeek$PeekSubscriber.onError(FluxPeek.java:221)
		at java.lang.Thread.run(Thread.java:834)
Caused by: io.netty.channel.AbstractChannel$AnnotatedConnectException: finishConnect(..) failed: Connection refused: localhost:8080
Caused by: java.net.ConnectException: finishConnect(..) failed: Connection refused
	at io.netty.channel.unix.Errors.newConnectException0(Errors.java:155)
	at io.netty.channel.unix.Errors.handleConnectErrno(Errors.java:128)
	at io.netty.channel.unix.Socket.finishConnect(Socket.java:278)
	at java.lang.Thread.run(Thread.java:834)

Results seen

The exception is logged on multiple lines. E.g.,

{ "message": "[2021-09-02 12:57:32:721] [sba-service_v1,,,] [\u001b[33mWARN \u001b[m] - [     parallel-1] d.c.b.a.s.s.InfoUpdater        - Couldn't retrieve info for Instance(id=4189dc1b3bbe, version=3, ....))\n",...}
{ "message": "java.util.concurrent.TimeoutException: Did not observe any item or terminal signal within 10000ms in 'map' (and no fallback has been configured)\n\tat reactor.core.publisher.FluxTimeout$TimeoutMainSubscriber.handleTimeout(FluxTimeout.java:295) ~[reactor-core-3.4.8.jar:3.4.8]\n\tSuppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException: \n",...}
{ "message": "\t|_ checkpoint ⇢ Request to GET info [DefaultWebClient]\n",...}
{ "message": "Stack trace:\n",...}

(the above example is truncated and formatted for readability)

Results expected

The exception should be combined into a single message.

Related defects

The example above also has the first line of logger output (e.g., [2021-09-02 12:57:32:721] [sba-service_v1,,,] ...) separate, which is caused by #73 and #79