Adding links to user & build stage in a Build message

What does this MR do?

Adds links to commit author and build stage in slack notifications

• Build the author_url and send it as part of the build message
  • If the author is a GitLab user, author_url is the GitLab user's url
  • else it is the mailto ref. of the author_email from git
• Use the build_id & author_url to construct links to the build & author

Are there points in the code the reviewer needs to double check?

• The location of where the author_url should be constructed. Was not sure if the data_builder/build.rb file is the correct place

Why was this MR needed?

For giving additional information about builds in slack notifications

Screenshots (if relevant)

Before:

After:

Does this MR meet the acceptance criteria?

• Changelog entry added
• 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 #26500 (closed)

Partially addresses #21114 (moved)