Yaml tests for standard retriever

[jdconrad]

This change does the following:

• renames the classic retriever to standard retriever
• adds support for (pre) filter to the standard retriever
• adds yaml tests for the standard retriever that covers all of the parse fields

[elasticsearchmachine]

Pinging @elastic/es-search (Team:Search)

[mayya-sharipova]

I realize we never talked about it, but should fields be a part of a retriever, similar how sort is a part of retriever? Or is this wrong to think this way because fields is applicable for the final fetch phase?

[jdconrad]

I think fields continue to make the most sense as a global value for the final result set because I don't know how you would resolve it in a simple way for multiple retrievers potentially.

[mayya-sharipova]

should the reason be about 8.13 version, may be we can say retrievers were added in 8.13?

[jdconrad]

Good catch! Fixed.

[mayya-sharipova]

@jdconrad Thanks Jack, the changes look good to me.

[jdconrad]

@mayya-sharipova Thanks for the review. I'll merge as soon as CI passes.