[DOC-META] Replace "indices" with "indexes"

[JeffHuss]

What do you want to do?

Existing documentation is inconsistent with references to "indices" and "indexes" often sitting right next to each other within the same page.

We'll need to review each page on an individual basis to determine whether the reference is hard coded into the OpenSearch product (e.g., the actual button in the interface says indices or a property in a configuration file must say indices), or if it's just part of the narrative.

For instances where indices is used, but it is not hard coded into the product, we should replace it with indexes.

List of PRs

[JeffHuss]

This issue can be used for tracking PRs and progress in making the edits. First step will be to identify where indices exists in the documentation when it is not referring to a hardcoded property called indices.

Once that's done, small PRs for individual changes would be optimal, maybe targeting one page at a time to reduce the likelihood of merge conflict.

[Naarcha-AWS]

Closing this in favor of #2358