[Internal]: Improve dense_vector and semantic_text index options documentation

[Mikep86]

Description

The index_options documentation for dense_vector and semantic_text fields should be improved to be more visible and provide more examples. These are the params users will use to enable new vector search data structures and quantization methods, such as DiskBBQ.

We should update the docs to provide:

• Clear, complete examples of how to use index_options to enable our latest and greatest vector search mechanisms (currently DiskBBQ)
• Better visibility into the index_options available for dense_vector fields
• Direct links from semantic_text docs to dense_vector index_options docs

Resources

Current semantic_text index_options docs: https://www.elastic.co/docs/reference/elasticsearch/mapping-reference/semantic-text#custom-by-parameters

Current dense_vector index_options docs (buried under "Properties of index_options"): https://www.elastic.co/docs/reference/elasticsearch/mapping-reference/dense-vector#dense-vector-params

Which documentation set does this change impact?

Elastic On-Prem and Cloud (all)

Feature differences

No environment differences

What release is this request related to?

9.2

Serverless release

N/A

Collaboration model

The documentation team

Point of contact.

Main contact: @Mikep86

Stakeholders: @benwtrent @kderusso @liranabn

[Mikep86]

PR to update the semantic search tutorial: #3854