Add support for neural search (text embeddings)

Still work in progress, but the idexing side of things work.

Thanks Janez. Looks like a great start. Besides the linting errors, I can see there are still a lot of hard coded values, and we're missing tests. I know it's a complex area, but it would be good to have some basic docs on setup and links for further info.

Quick n dirty review for now as this is obviously still WIP - great to see movement in this area though!

slashrsm → changed the visibility of the branch query_side to hidden.

After watching Driesnote and looking into AI module → a bit I realized that we are basically re-implementing their provider plugins here. In order to avoid that I decided to depend on the AI module for providers. Updated MR assumes/uses ✨ Provide embeddings vector size Active , which add vector size function that we rely on.