Small improvements on the ES field cap endpoint

• if one of the index patterns doesn’t match anything, we should return a 200: we should call check_all_index_metadata_found method in the root function (as it's done for a classic search endpoint
• return undocumented type value
• /_field_caps URL

Query Parameters

• fields
• allow_no_indices (ignored)
• expand_wildcards (ignored)
• accept ignore_unavailable query parameter and ignore it silently
• include_unmapped parameter
• types parameter
• filters parameter

Start by locating the ES field cap endpoint and reviewing how the checked query parameters are handled, especially the documented behavior for unmatched index patterns and the type value. Then trace the remaining include_unmapped, types, and filters parameters and verify that the endpoint accepts them with the intended field-cap response behavior.