Client-agnostic RPC runtime for Ash.
An extension decorates an Ash.Info.Manifest with AshRpc.Manifest.Decorator
(driven by an AshRpc.MappingSource), defines an AshRpc.Profile, and mounts
an endpoint that calls AshRpc.run_action/4 / AshRpc.validate_action/4, or
uses AshRpc.Plug / AshRpc.Channel.
plug and phoenix are optional; AshRpc.Plug and AshRpc.Channel only
compile when they are available.