Support setting global image registry in Spamcheck chart

What does this MR do?

Iterative implementation of !2415 (closed)

commit 799d4f0a (HEAD -> global-image-settings, origin/global-image-settings) Author: Mitchell Nielsen mnielsen@gitlab.com Date: Wed Jul 12 17:15:43 2023 -0500

Add tests for new image templates

Adds tests for the new image templates, initially testing
Spamcheck specifically.

commit 061887da Author: Mitchell Nielsen mnielsen@gitlab.com Date: Wed Jul 12 17:14:22 2023 -0500

Implement new image templates in Spamcheck chart

Implements the new image templates in the Spamcheck chart.
This was selected for initial implementation as it is disabled
by default.

Changelog: added

commit 820db5ec Author: Mitchell Nielsen mnielsen@gitlab.com Date: Wed Jul 12 15:32:12 2023 -0500

Add new image helper templates

Adds in new image helper templates that assist with
calculating the full image path. These will iteratively replace
the values in `image:` fields and allow setting repository and/or
registry globally.

commit c15a9377 Author: Mitchell Nielsen mnielsen@gitlab.com Date: Wed Jul 12 14:44:35 2023 -0500

Move image-related templates to dedicated file

Moves all image-related templates from helpers.tpl
to a new file named images.tpl for better organization.

Related issues

Related to #2859

Testing

You can try different permutations of configs between global.image and gitlab.spamcheck.image. There's also rspec tests added.

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.