Update sources from the API

[rdettai]

Is your feature request related to a problem? Please describe.
Updating a source is currently not possible. It would be very valuable because some paramters like the transform or the num_pipelines might need to evolve through time.

Describe the solution you'd like
A REST endpoint

PUT api/v1/indexes/<index id>/sources/<source id>

Like the index update, the body would be a full source config file (json or yaml):

• it would only be valid to update some specific fields: num_pipelines, transform, params
  • updating params is a footgun for some source types, but it's still valuable (e.g update kafka ssl settings)
• source_id and source_type cannot be updated.

Describe alternatives you've considered
Recreating a source with the new params is usually not a good idea because you would loose the checkpoints.

Additional context
NA