feature - transformer plugins

[JarbasAl]

allow the usage of utterance/metadata transformers in hivemind-core before forwarding the utterance to OVOS

as an example https://github.com/JarbasHiveMind/ovos-user-id could be used to assign a user coming from a voice satellite, or more relevantly, a hivemind bridge could map users from a chat service to a internal user_id (eg, from matrix chat)