Add new local_store config for Pages

What does this MR do?

(this is my first MR to gitlab-org/omnibus-gitlab 🎉 so I may have missed a few things.)

This MR adds a new local_store config node for Pages, in config/gitlab.yml, following some work done on gitlab-org/gitlab in this MR.

The changes made here are based on these instructions.

Related issues

gitlab#301159 (closed)

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 the dev.gitlab.org mirror for this branch 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