Add sentry configuration options for GitLab KAS

What does this MR do?

This MR adds new gitlab_kas['sentry_dsn'] and gitlab_kas['sentry_environment'] configuration options, allowing to enable Sentry error tracking for GitLab KAS. It supports setting the Sentry DSN as well as an optional environment, as it's also the case for other GitLab services. GitLab KAS configuration reference: https://gitlab.com/gitlab-org/cluster-integration/gitlab-agent/-/blob/master/pkg/kascfg/config_example.yaml#L55

Closes #5738 (closed)

Related issues

• #5738 (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 dev.gitlab.org if the change is touching anything besides documentation or internal cookbooks -> how to check via Community contribution?
• trigger-package has a green pipeline running against latest commit -> how to check via Community contribution?

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added -> Existing tests updated
• [-] Integration tests added to GitLab QA -> KAS setup not being tested within gitlab-org/gitlab-qa
• [-] Equivalent MR/issue for the GitLab Chart opened -> Configuration already possible via KAS customConfig