Modify response for PUT /{source}/:id/members/:user_id for promotion scenario

Edit a member of source (doc) (code)

• PUT /groups/:id/members/:user_id
• PUT /projects/:id/members/:user_id
• Returns a member json
• Also used to add custom-role (doc)(doc)

TODO: Need to validate and return a meaningful response when member gets queued.

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Implementation: Update API and docs to account for non-billable... (!167020 - merged)