Add 'get_supported_features' RPC for data explorer backend

[wesm]

Addresses #2201. This is just a starting point and will be refined to add more granular feature flagging, but wanted to break the seal on this.

Summary

• Adds feature flags for search_schema, set_row_filters, and get_column_profiles
• For filtering and profiles, indicates which row filter types / profile types are supported
• Return basic feature flags for pandas objects (each type of data structure can return different feature flags, so it isn't necessarily global to the runtime but rather local to the particular data type)
• Extracted row filter type and profile type into shared enums

Also addresses #2599 (renaming search_filter_params.type to search_type)

Associated amalthea PR: posit-dev/ark#298

[jmcphers]

Thanks for fixing this too!