Integrate Apache Ratis to help manage Raft status

We have some discussions about the integration of Apache Ratis in RP: https://github.com/apache/iotdb/pull/3939.

Create a new issue here to let more people join.

https://github.com/apache/iotdb/pull/3939#issuecomment-917955815

https://github.com/apache/iotdb/pull/3939#issuecomment-917961701

https://github.com/apache/iotdb/pull/3939#issuecomment-917983405

Update the reasons why I'd like to import a 3rd party Raft library.

- First and the important one, raft implementation in IoTDB can't guarantee the correctness (I mean consensus part, even only for write). We have found and fixed some bugs about Raft and we are not sure the end of this. Just like @LebronAl said, the devil lies in the corner cases. It's very hard for us to construct a systematic UT/IT/Manual tests to ensure the safe properties of Raft. As for performance affect, my understanding is even the fastest vehicle should be saft. And raft is only a small part of system, I think if we can use the 3rd party library properly, performance loss should be very small.

- Second, current implementation of Raft mixed together with application logic which is hard to maintain and understand.

- Last but not least, apply 3rd party library could release us from detail of Raft and focus on core engine improvement, building IoTDB ecosystem, etc.

Beginne mit dem Lesen der Diskussion im Pull Request 3939 und der verlinkten Kommentare zum Importieren von Apache Ratis. Das Issue nennt keine Implementierungsdateien, Tests, Integrationsgrenzen oder Akzeptanzkriterien; ein abgestimmtes Design und definierte Abschlusskriterien sind erforderlich, bevor mit der Implementierung begonnen werden kann.

Vom Indexierungsmodell aus dem Issue-Text verfasst.