Clearly show who triggered the pipeline in pipeline successful/failed email

What does this MR do?

There was some confusion about to whom the pipeline succeeded/failed email was sent because the commit author, commit committer and pipeline triggerer can be 3 different people. So show in the email clearly:

• Commit author
• Committed by (if different from author)
• Pipeline triggered by

Screenshots

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #28755 (closed)

cc @dimitrieh @godfat @ayufan @zj