UI/Webserver: Expose an endpoint to which a user should be redirected after granting Oauth consent

[sherifnada]

Once a user grants consent and is redirected back to airbyte, they should be redirected to an endpoint which will do the following:

1. call complete_auth_request on the backend server, providing the following inputs:
   1. connector definition ID
   2. current workspace ID
   3. any query params found in the redirect URL
2. complete_auth_request will return an object containing some properties related to oauth e.g: {refresh_token: XYZ, access_token: XYZ, ...}. Using this response, the UI should pre-fill any fields with the same name. For example, if the spec has only {refresh_token: {type: string}} then the UI should pre-fill that field with the value returned from the API.
3. Display the spec as normal and allow the user to fill it out like normal

The below diagram illustrates how this would work. See the portion after "Redirect user to airbyte with auth code".