External service use for BYON

[costinm]

The current ExternalService seems like a perfect fit for BYON (allow use of custom names,
backed by specified services), but may need additional documentation/fields to clarify how internal
services or destinations can be added to the set. I'm not sure if there is a better place in the new API to define this.

[costinm]

So far the agreement is to move ahead with the current names, and add/extend if needed.