Add warning on Java language binding that it isn't maintained

[nirroz93]

Describe the bug

The doc doesn't refer to the fact that Java library isn't maintained (https://github.com/fluent/fluent-logger-java last updated 4.5 years ago, issue fluent/fluent-logger-java#99 left unanswered),

Link to the problematic documentation

https://docs.fluentd.org/language-bindings/java

Expected explanation

Add a note that the library isn't maintained (or up for adoption)

Additional context

No response

[Watson1978]

We need some action for this issue...

[kenhys]

Does it better to recommend https://github.com/komamitsu/fluency?