Search API Index fields need more attributes

Going to start with just mocking up UI changes as discussed in Slack. Something like this:

Then also trying to provide clarity as to the 3 things:

1. Main content: This is the main body content. It is typically longer and needs to be broken into chunks. Queries by end-users are performed on this content.
2. Contextual content: The main body on its own, when chunked, can often miss its overall context. Repeating contextual details into each chunk, such as title, summary, or authors can help provide better results for queries. This content is therefore appended to each chunk of 'Main content' and therefore queries by end-users also use this context to provide better results.
3. Filterable attributes: This content is attached to the record to allow the Vector Database to pre-filter results (such as only search within a specific date range, or on a specific taxonomy term) before searching for relevant content. This allows the end-users' query to be run against a sub-set of the Vector Database only.

Main content being formerly captured by 'Embeddings' field type.

Needs an update hook to convert the old field type.

Okay first draft

Not working, but let's review before making this function

scott_euser → credited yautja_cetanu → .

Updated issue summary

Updated all the texts on the embedding strategy form to match the Field indexing configuration and put things more into lay person terms (particularly in field descriptions).

With everything having defaults, much less intimidating:

Then if you do decide to open the embedding strategy, more lay-person terminology/explainers added.

Added comments to explain the various changes so its easier to review. Ready for review now. Thanks!

Automatically closed - issue fixed for 2 weeks with no activity.