Experimental opensearch self query (self query retriever + query constructor)

[t0mpl]

PR Checklist

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• Name your Pull Request title clearly, concisely, and prefixed with the name of the primarily affected package you changed according to Good commit messages (such as memory: add interfaces for X, Y or util: add whizzbang helpers).
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[tmc]

@ThomasP1988 can you shore this up and mark it ready for review? (or are you seeking a review in the current draft state?)

[t0mpl]

unfortunately it's still far from being finished, this is a big piece of work but just sharing progress in case I take a wrong decision or something needs to be discussed

[tmc]

@ThomasP1988 why close this?

[t0mpl]

I will open another one soon, but i'm adding a schema detector + an example for semi structured rag on opensearch, almost done but need some more work