Deprecate the "Master" nomenclature

[tlfeng]

Is your feature request related to a problem? Please describe.
OpenSearch repository is going to replace the terminology "master"with "cluster manager".
issue: opensearch-project/OpenSearch#472 (comment), with the plan for its terminology replacement.

Although the existing usages with "master" will be supported in OpenSearch version 2.x to keep the backwards compatibility, please prepare for the nomenclature change in advance, and replace all the usages with "master" terminology in the code base.
All the OpenSearch REST APIs and settings that contain "master" terminology will be deprecated in 2.0, and alternative usages will be added.

Describe the solution you'd like
Replace the terminology "master" with "cluster manager".

When being compatible with OpenSearch 2.0:

• Replace "master" in code comment and internal variable / class name.
  Specifically, internal class name https://github.com/opensearch-project/anomaly-detection/blob/1.3.1.0/src/main/java/org/opensearch/ad/cluster/MasterEventListener.java

When being compatible with OpenSearch 3.0:

• Replace "master" in the reference to OpenSearch Java API
  (most of the new APIs are available in version 2.2, except AcknowledgedResponse)
  • import org.opensearch.cluster.LocalNodeMasterListener -> LocalNodeClusterManagerListener
  • clusterManagerService.onMaster() / offMaster() -> onclusterManager() / offClusterManager()
  • DiscoveryNodes.Builder().masterNodeId() -> clusterManagerNodeId()
  • import org.opensearch.action.support.master.AcknowledgedResponse -> import org.opensearch.action.support.clustermanager.AcknowledgedResponse (will be available in version 3.0)

Describe alternatives you've considered
None.

Additional context
None.

[amitgalitz]

I began this process by replacing any variable, logs or comments with the use of "master" to "clusterManager" (#504). This process will continue when Opensearch Core makes further changes to classes and methods that AD is using with this terminology.

[dblock]

For 2.0, at a minimum please ensure that the plugin is not calling any deprecated APIs in core or another plugin, and confirm below, then remove the 2.0.0 label. If you have time, do the complete deprecation as described in this issue.