Add proxy policy support

What does this MR do?

Adds support for configuring gitlab-org/gitlab-shell!619 (diffs) in the charts.

This merge request also enables nginx-ingress to use the PROXY protocol by default if gitlab-sshd is enabled, unless the reject policy is used.

Related issues

Related gitlab-org/gitlab-shell!619 (diffs)

Related gitlab-org/gitlab-shell#548 (closed)

Related https://gitlab.com/gitlab-org/gitlab/-/issues/361755

Related https://gitlab.com/groups/gitlab-org/-/epics/8014

Related #2933

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
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for omnibus-gitlab opened