Add prometheus to dependency automation

What does this MR do?

Adds prometheus to the dependency automation, so we start getting MRs automatically when there are updates

Testing

1. Download the deps cli if you have not already - https://www.dependencies.io/quickstart/
2. CD into your checkout of the omnibus project and checkout this branch
3. Run deps upgrade
   • The latest prometheus update should be one of the actions it pulls in for you to approve.
4. Tell it to apply the prometheus upgrade
5. Confirm that it changed the prometheus software file as expected (you can discard this change after)

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion

Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• Pipeline is green on dev.gitlab.org if the change is touching anything besides documentation or internal cookbooks
• trigger-package has a green pipeline running against latest commit

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for the GitLab Chart opened