Break down `templates/_checkConfig.tpl` into smaller files

What does this MR do?

This MR is to split the big templates/_checkConfig.tpl and the corresponding test file file into smaller files. The tpl file is split into a handful of templates/_checkConfig_xyz.tpl, where xyz is a group name. Each group has a corresponding test file, located at spec/integration/check_config/xyz_spec.rb. Miscellaneous checks are still kept in the original big files until there are enough checks of the same type to form a group.

In detail, 7 new groups are formed, in alphabetical order: geo, gitaly, mailroom, postgresql, registry, sidekiq, webservice.

Regardless of the file changes, there are no modifications to the functionalities, nor the checks. It contains code splitting only.

Related issues

Closes #2676 (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

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes. This MR doesn't introduce any functionality change.
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA N/A
• Equivalent MR/issue for omnibus-gitlab opened N/A