Reviewer request: [IGNITE-13144] Improve ClusterState enum and other minor improvements for the cluster read-only mode.

[Sergey Antonov]

Hello, Igniters!

I'd like to get a review of the ticket [1]. The patch is ready [2].
Can someone look at it, please?

[1] https://issues.apache.org/jira/browse/IGNITE-13144
[2] https://github.com/apache/ignite/pull/7924

-- 
BR, Sergey Antonov