Add sparse_vector field type

[carlosdelest]

Add sparse_vector field support (added to Elasticsearch elastic/elasticsearch#98996) to mappings, and include it as usable in the docs for text_expansion query.

[pquentin]

Thanks! LGTM.

By the way I think the documentation is missing for that field in the Elasticsearch docs. I can see rank_feature but not sparse_vector: https://www.elastic.co/guide/en/elasticsearch/reference/master/rank-feature.html

[carlosdelest]

I think the documentation is missing for that field in the Elasticsearch docs

Thanks for looking into that @pquentin ! It's just been merged in elastic/elasticsearch#100348 👍