[POC] Adding Orchestrate API and Search Response Processor Step

[joshpalis]

Description

Adds a new /_plugins/_flow_framework/<workflow_id>/_orchestrate API which accepts a map of string to string as the request body content.

Example payload looks like :

POST _plugins/_flow_framework/<workflow_id>/_orchestrate 
{
    "model_id" : "uuihhqw0f9i90932r1h0a9w0f"
}

The transport action retrieves this along with the workflow ID to fetch a previously created search use case template from the global context index. The process nodes are then created, passing in the request body content map for substitution and then executes the graph.

Upon attempting to complete each plain action future, we track the final returned search response to return to the user

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[joshpalis]

Tests will fail since since the getters for the request and response processor factories are package private :

> Task :compileJava
/__w/flow-framework/flow-framework/src/main/java/org/opensearch/flowframework/workflow/SearchResponseProcessorStep.java:85: error: getResponseProcessorFactories() is not public in SearchPipelineService; cannot be accessed from outside package
                .getResponseProcessorFactories();
                ^

Modifying this line in the SearchPipelineService so that the getter is public and publishing to maven local will allow the tests to pass locally

[owaiskazi19]

LGTM