Rename reserved node id '_must_join_elected_master_' to '_must_join_elected_cluster_manager_' that used by in DetachClusterCommand

[tlfeng]

Description

To support inclusive language, replace "master" with "cluster manager".

• Replace public field MUST_JOIN_ELECTED_MASTER with MUST_JOIN_ELECTED_CLUSTER_MANAGER in VotingConfiguration class
• Rename the preserved node id _must_join_elected_master_ to _must_join_elected_cluster_manager_

The original _must_join_elected_master_ is only used as a preserved node id for "Detach Cluster Command" (https://github.com/opensearch-project/OpenSearch/blob/1.3.1/server/src/main/java/org/opensearch/cluster/coordination/DetachClusterCommand.java#L89).
"Detach Cluster Command" ./bin/opensearch-node detach-cluster can detach a node from its cluster by resetting its cluster UUID. The node can then join another cluster with a different UUID. _must_join_elected_master_ is set as a node id and used as an identifier for the node processed by "Detach Cluster Command".
Reference: https://www.elastic.co/guide/en/elasticsearch/reference/7.10/node-tool.html#node-tool-detach-cluster

Issues Resolved

A part of #1548 , #1684

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff

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[opensearch-ci-bot]

❌   Gradle Check failure 43e6389
Log 4872

Reports 4872

[opensearch-ci-bot]

✅   Gradle Check success 01b9d94
Log 4887

Reports 4887

[dblock]

I assume this name is never used in a distributed manner where 1 node calls it _must_join_elected_cluster_manager_ and the other _must_join_elected_master_ and it's ok?

[tlfeng]

Hi @dblock , thanks for your review!
In my opinion, the preserved node id _must_join_elected_master_ is only read by ClusterFormationFailureHelper, which result a line of log generated. The log says "master not discovered yet and this node was detached from its previous cluster", so it looks like not used in a distributed manner.

[tlfeng]

Alright, to make it safe, it's better for me to deprecate MUST_JOIN_ELECTED_MASTER first in version 2.x, and accepting the both _must_join_elected_cluster_manager_ and _must_join_elected_master_ in ClusterFormationFailureHelper.
Otherwise, maybe doing a rolling upgrade from 2.x to 3.x after running ./bin/opensearch-node detach-cluster will be a problem to identify the old identifier _must_join_elected_master_. Thank you! 😄

[tlfeng]

Created backport PR #3138 to deprecate VotingConfiguration.MUST_JOIN_ELECTED_MASTER in 2.x version