[DOC] New docs for Search Pipelines SplitResponseProcessor

[dbwiddis]

What do you want to do?

• Request a change to existing documentation
• Add new documentation
• Report a technical problem with the documentation
• Other

Tell us about your request.

I'm adding a Split Response Processor to Search Pipelines. It will need to be documented. I'll do the documentation.

*Version: 2.16.0

What other resources are available?

Issue requesting this:

• [Feature Request] Build Sort Search Processor and Split Search Processor OpenSearch#14758

PR implementing this:

• Add SplitResponseProcessor to Search Pipelines OpenSearch#14800