[DOC] New Search Processors (collapse, oversample, truncate_hits)

[macohen]

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. Provide a summary of the request and all versions that are affected.
New in 2.11 and should be placed here: https://opensearch.org/docs/latest/search-plugins/search-pipelines/search-processors/

The ability to create processors that can share data, plus three new processors are in the PR attached to the issue below. The three new search processors are type:

1. "collapse" - given a field name, this response processor will find all fields with the same value within the returned results and collapse results on that value
2. "oversample" - given a "sample_factor" (double >= 1.0) and "original_size" (the size of results originally requested at query time), this request processor will fetch sample_factor * original_size search hits from the index. This is useful for such operations as reranking results or other manipulation where the BM25 similarity scores may not be enough to produce desired results.
3. "truncate_hits" - this response processor will reduce the number of hits returned in a response to "target_size" (integer >=0). This is useful when using "oversample" to reduce the number of hits to no more than what the original request expected.

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.
opensearch-project/OpenSearch#6722

cc:@msfroh