[DOC] Update documentation for ignore_unavailable within search related APIs

[jainankitk]

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.
Related to OpenSearch#12371 and OpenSearch#13298

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.

[hdhalter]

Thanks, @jainankitk. Should this be backported to 2.13?

[jainankitk]

Should this be backported to 2.13?

No, we don't need to backport 2.13. Will go out in 2.14

[jainankitk]

@hdhalter - Should we mark this completed once the PR is merged!?

[hdhalter]

@hdhalter - Should we mark this completed once the PR is merged!?

It's in the 'done, waiting to merge' state, so technically we can merge it anytime (it merges into a staging branch until the official release). It's mostly for my own reporting. :)