Replace "master" terminology in code comments, and internal variable, method and class names

[tlfeng]

Is your feature request related to a problem? Please describe.
Replace "master" terminology in the code base, but only the places that won't impact the backwards compatibility.

A part of #472

Describe the solution you'd like
Replace all the "master" terminology in the following location:

• "master branch" in documents
• code comments
• internal variable, method and class names

Any APIs or configurations will not be impacted.

Directories:

• server
• • server/src/main (PR: Replace internal usages of 'master' term in 'server/src/main' directory #2519)
• • server/src/test (PR: Replace internal usages of 'master' term in 'server/src/test' directory #2520)
• • server/src/internalClusterTest (PR: Replace internal usages of 'master' term in 'server/src/internalClusterTest' directory #2521)
• client (PR: Replace internal usages of 'master' term in 'client' directory #3088)
• modules (PR: Replace 'master' terminology with 'cluster manager' in 'modules' directory #3328)
• plugins (PR: Replace 'master' terminology with 'cluster manager' in 'plugins' directory #3329)
• qa (PR: Replace 'master' terminology with 'cluster manager' in 'qa' directory #3330)
• test (PR: Replace internal usages of 'master' term in 'test' directory #3283)

The issue to track "master" word in Log messages: #2539

There are 3 usages with "master" terminology in server directory that need to be replaced in caution:

• _BECOME_MASTER_TASK_ https://github.com/opensearch-project/OpenSearch/blob/1.3.1/server/src/main/java/org/opensearch/cluster/coordination/JoinTaskExecutor.java#L107 (PR: Rename BecomeMasterTask to BecomeClusterManagerTask in JoinTaskExecutor #3099)
• _must_join_elected_master_ https://github.com/opensearch-project/OpenSearch/blob/1.3.1/server/src/main/java/org/opensearch/cluster/coordination/CoordinationMetadata.java#L354 (PR: Rename reserved node id '_must_join_elected_master_' to '_must_join_elected_cluster_manager_' that used by in DetachClusterCommand #3116)
• no master https://github.com/opensearch-project/OpenSearch/blob/1.3.1/server/src/main/java/org/opensearch/cluster/coordination/NoMasterBlockService.java#L48 (PR: Rename ClusterBlock description 'no master' to 'no cluster-manager' #3133)

Describe alternatives you've considered
None.

Additional context
None.

[tlfeng]

Nearly all the usage of master terminology in internal variable, method and class names have been replaced by cluster manager, so close the issue.