Add general purpose gitlab-toolbox upkeep cronjob

What does this MR do?

Add a template for a cronjob object nicknamed 'upkeep' to consistently execute any general purpose activity customers may want to leverage to gitlab-toolbox to perform. This change in product direction was the result of discussions on this related Merge Request: !2618 (closed)

Related issues

Closes #3350

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
• When ready for review, MR is labeled "~workflow::ready for review" per the Distribution MR workflow

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 omnibus-gitlab opened
• Validate potential values for new configuration settings. Formats such as integer 10, duration 10s, URI scheme://user:passwd@host:port may require quotation or other special handling when rendered in a template and written to a configuration file.