Add bulk publish endpoint to Draft Notes API

What does this MR do and why?

Adds a basic endpoint ro the Draft Notes API for bulk publishing all pending draft notes on a given merge request that are authored by the user.

Screenshots or screen recordings

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #396965 (closed)