Hub SSOT - How we blend the current discovery.yml and the current singer spec yaml files

We want to the V2 hub API to serve both the current discovery contents and the Singer definitions, to do that we need to blend the two schemas into a generic shared schema for all plugins.

Things to consider:

• Extra Singer metadata meltano_sdk, maintenance_status, etc.
• Singer definitions are missing settings and group validations in many cases
• Singer definitions dont have a schema version like the discovery does