List all types supported by each agg

[nik9000]

Some aggregations list which types they can operate on but some don't. Sometimes they say things like "this works for keywords and all of the types that usually work for bucket aggregations". I think it'd be cleaner if we just listed all of the types supported by the agg out explicitly. I think we should say "this works for numbers, keywords, dates, ip addresses, geo_points, geo_shapes, and foo". We often have to explicitly make the aggregation work with each new type so we may as well update the docs too. I guess "numbers" is kind of a different case - most aggs have a single implementation for "numbers". But I think it's pretty natural to just say "numbers" in the list.

[elasticmachine]

Pinging @elastic/es-analytics-geo (Team:Analytics)

[elasticmachine]

Pinging @elastic/es-docs (Team:Docs)

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)