Would like to be able to specify the source of a custom activity type that's been created via the API. This is important because we're about to import hundreds of activity types and would like to have them siloed by source.

When filtering by activity types, being able to select all the activities under a specific source is incredibly helpful. In the future we'd like to be able to select all the activities sourced from amplitude for example. This however isn't realistic since all custom activities get aggregated to custom.