Update email templates to use linked file links
<!--IssueSummary start--> <details> <summary> Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards. </summary> - [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=580453) </details> <!--IssueSummary end--> We should update links in email templates that point to Rapid Diffs pages. These links should be updated: 1. Diff file 2. Diff line 3. Diff discussion All of these should contain `?file_path=<file_path>` in addition to the existing URL fragment.
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