Consider 'global.gitlabVersion' in helper image tags, replace use of digests

What does this MR do?

• When global.gitlabVersion is set, use that value for the helper image tags (alpine-certificates, kubectl, cfssl-self-sign)
• Removes usage of digests to reference a specific version of the helper images
• Respect tagSuffix in the helper image tags
• Remove redundant tagSuffix values for FIPS and UBI examples (now that tagSuffix is respected)

Related issues

Depends on #4075 (closed)

Closes #3717 (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
• 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.