Add auth config to oauth api

[ChristopheDuong]

What

New OAuth flows will need values from the connector config in #6971

How

Alteernative to #7678

This API changes adds an "optional" auth config parameter to the API endpoint to be potentially used during oauth flows (depends on flow implementation)

Context

• When FE calls the completeOauth API endpoint, a auth config is built with values extracted from a partial connector config if any fields is used as input fields to the oauth flow
• once oauth flow is completed, the backend returns the oauth outputs inside the auth config. The Front-end would have to merge this config back to the connector config where it needs to (as declared in the rootObject in auth spec object).
• Once merged, FE can continue with the modified connectionConfig to SourceCreate when clicking on "setup connection"

[sherifnada]

I like this approach a lot. It's very well-scoped to the inputs required for oauth. I'd go for this one over #7678

[jamakase]

Have some questions:

1. How will it handle airbyte_secret fields?
2. I believe we don't yet have file upload, but what if we have it at some point, won't it break this endpoint? Though if we upload file initially and then just send ids - it should be fine. But we need to consider such a case in advance.

I understand that this prop is just additional and we are free to send everything we want here, but the problem is that we can't send exact connectorConfiguration property as it may be not valid yet, so there is a possibility that we will send some temp frontend state.

[ChristopheDuong]

Have some questions:
I understand that this prop is just additional and we are free to send everything we want here, but the problem is that we can't send exact connectorConfiguration property as it may be not valid yet, so there is a possibility that we will send some temp frontend state.

In this PR, we changed our minds and instead of sending connectorConfiguration, we'll be restricting to build a new config object authInputConfiguration with only fields that are needed by the OAuth flow as described in its Input Specification node.

[cgardens]

Awesome! Thanks for the short PR with just the iface change!