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 the reference to OpenSearh setting:
  Replace setting name cluster.initial_master_nodes with cluster.initial_cluster_manager_nodes in .github/configurations/docker-compose.yml

Describe alternatives you've considered
None.

Additional context

[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.

[amitgalitz]

Removed all uses of master except for cases where its part of link to a Github branch that has master label in branch. No prior uses of blacklist or whitelist

[amitgalitz]

Closing this issue as there are no uses of blacklist or whitelist in repo. Only uses left of master are in links to Github branches that were named master, in old release notes if a PR had it in the name and for importing link checker workflow (lycheeverse/lychee-action@master). Feel free to re-open if more effort needs to be put on changing the links somehow.