[FEATURE] Add specs for search processors

[dblock]

Is your feature request related to a problem?

OpenSearch supports a number of search request/response processors. Tests tests were added in #505.

What solution would you like?

Add specs and tests for the remaining processors.

Do you have any additional context?

Part of #168.

[Tokesh]

Hello :)
As I understand it, all that remains from the specs is to add ml_inference, neural_sparse_two_phase_processor and tests for them?

[dbwiddis]

As I understand it, all that remains from the specs ...

There should be tests written to cover as many of the processors as possible as well; these do not yet exist and were what I was planning on doing when I self-assigned.

I'm not sure which namespace we should use for plugin-added processors which may or may not be available.

[navneet1v]

@dblock adding to the scope of this issue, Opensearch also supports SearchPhaseResults Processors. So when we pick this GH issue lets ensure that we are picking up spec for PhaseResultsProcessors too. Ref: https://opensearch.org/docs/latest/search-plugins/search-pipelines/normalization-processor/