Implement TransportNodesAction equivalent for SDK

[vibrantvarun]

Is your feature request related to a problem?

TransportNodesAction is an abstract class in OpenSearch. This class is been inherited by many transportActions in the AnomalyDetector plugin. It accepts 4 parameters mentioned below.

1. NodesRequest extends BaseNodesRequest,
2. NodesResponse extends BaseNodesResponse,
3. NodeRequest extends TransportRequest,
4. NodeResponse extends BaseNodeResponse

For extensions, we need to extend TransportAction abstract class in all classes which has transportAPI code in AD.
TransportAction accepts 2 parameters

1. Request extends ActionRequest,
2. Response extends ActionResponse

Therefore, there is a need to make TransportNodesAction equivalent for SDK as well.

What solution would you like?

The issue requires us to

• Cater all the classes which extend TransportNodesAction.
• Create a TransportNodesAction for SDK and implement the same level of functionality which it currently has.
• Test the Sanity of the API's for extensions and compare there response with plugins
• Document the changes

[dbwiddis]

Key point here is this class of requests are intended to query information on multiple OpenSearch nodes. In the Extension enviornment we don't have all those nodes present so we would need to (possibly?) query the information via some REST API equivalent. Classic example may be a NodesStatsRequest to get Indexing pressure (see #655).

So we may want to create a local SDK transport action that queries OpenSearch via REST API for data like this. A general abstract superclass will allow for other similar requests to node stats.