[Internal]: Document all of the ways to update ES settings

[shainaraskas]

Description

Do a better job of explaining how settings can be set / overridden / reset, impact of JSON parsing order

Raised in elastic/elasticsearch-specification#4435, behavior outlined in https://docs.google.com/document/d/1DqkEMTCyJsFArJP_ePj4zFsuTx2-0UNsH4NGmjg00yQ/edit?tab=t.0#heading=h.vwpq1kn6hahn

Impacts both cluster + index settings

Resources

https://docs.google.com/document/d/1DqkEMTCyJsFArJP_ePj4zFsuTx2-0UNsH4NGmjg00yQ/edit?tab=t.0#heading=h.vwpq1kn6hahn

Content up to, but not including "How to model index settings in the API specification?"

Which documentation set does this change impact?

Unknown

Feature differences

What release is this request related to?

N/A

Serverless release

Collaboration model

The documentation team

Point of contact.

Main contact: @pquentin