Integrate with elastic search plugin

[splitbrain]

Theoretically ElasticSearch can be used as a vector storage. It would be cool if we could use that when the ElasticSearch plugin is installed.

• seems like we can store multiple chunks per document like so: https://www.elastic.co/search-labs/blog/multi-vector-relevance
• would we still rely on the search index' page.idx?
• could we surface the similarity search in search results as well?
• could the bot also use indexed media?
• does the Elastica lib support all this new vector stuff?
• the disability to store negative values seems weird: https://junming-chen.medium.com/using-elasticsearch-as-a-vector-database-dive-into-dense-vector-and-script-score-198e2eb807d6