RATIS-2589. Fix Javadoc warnings

[adoroszlai]

What changes were proposed in this pull request?

• Fix Javadoc warnings.
• Fail compile check on Javadoc warnings, except with version 1.8, which reports the following false positives:

ratis-server-api/src/main/java/org/apache/ratis/statemachine/StateMachine.java:375: warning - Tag @link: can't find link(DataStream, LogEntryProto) in org.apache.ratis.statemachine.StateMachine.DataApi
ratis-server-api/src/main/java/org/apache/ratis/statemachine/StateMachine.java:232: warning - Tag @link: can't find notifyServerShutdown(RoleInfoProto, boolean) in org.apache.ratis.statemachine.StateMachine.EventApi
ratis-server-api/src/main/java/org/apache/ratis/statemachine/StateMachine.java:265: warning - Tag @link: can't find notifyFollowerSlowness(RoleInfoProto, RaftPeer) in org.apache.ratis.statemachine.StateMachine.LeaderEventApi
ratis-grpc/src/main/java/org/apache/ratis/grpc/util/ZeroCopyMessageMarshaller.java:222: warning - Tag @link: can't find release(T) in org.apache.ratis.grpc.util.ZeroCopyMessageMarshaller

https://issues.apache.org/jira/browse/RATIS-2589

How was this patch tested?

https://github.com/adoroszlai/ratis/actions/runs/28638905538

[szetszwo]

@adoroszlai , thanks for working on this! Just a comment inlined.

[szetszwo]

Let's use » and « . It will be easy to read the javadoc in the source.

[adoroszlai]

Thanks for the hint, it really reads better.

[szetszwo]

+1 the change looks good.