Change 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, with the plan for its terminology replacement.

Although the existing usages with "master" will be supported in OpenSearch version 2.x until further notice to keep the backwards compatibility, it's suggested to prepare for the nomenclature change in advance, and replace all the usages with "master" terminology in the code base.

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.

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 AcknowledgedRequest and AcknowledgedResponse)
  • updateSettingsRequest.masterNodeTimeout -> updateSettingsRequest.clusterManagerNodeTimeout
  • openIndexRequest.masterNodeTimeout() -> openIndexRequest.clusterManagerNodeTimeout
  • import org.opensearch.action.support.master.MasterNodeRequest -> import org.opensearch.action.support.clustermanager.ClusterManagerNodeRequest
  • import org.opensearch.action.support.master.TransportMasterNodeAction -> import org.opensearch.action.support.clustermanager.TransportClusterManagerNodeAction
  • import org.opensearch.action.support.master.AcknowledgedRequest -> import org.opensearch.action.support.clustermanager.AcknowledgedRequest (will be available in version 3.0)
  • 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

[naveenpajjuri]

Renamed master to Cluster Manager where ever possible in variable, class names and updated the documentation accordingly.

[tlfeng]

After searching the keyword in the repository through GitHub, I found there are several Java APIs still need to be replaced before version 3.0, and I updated in the issue description, please take a look at. Thank you 👍