Decouple service types and 3rd party service development

[yaruno]

Is your feature request related to a problem? Please describe.

Plugin system has been decoupled from the development of the elizaos main repo, but developing new service extensions is still dependent on upkeeping the service type definitions located under core package types.

Describe the solution you'd like

Decouple definition of service types e.g. like clients and plugins have been decoupled from the main code repository.

Describe alternatives you've considered

Additional context