Support configuring Gitaly server side backup URL

What does this MR do?

Support configuring Gitaly server side backups

Allow to configure the object storage URL used for server side Gitaly backups.

Gitaly docs: https://docs.gitlab.com/ee/administration/gitaly/configure_gitaly.html#configure-server-side-backups

Changelog: added

What it does not

1. Add support for server side backups in the CNG backup-utility. (This is being implemented in gitlab-org/build/CNG!1785 (merged)).
2. Add documentation on how to use server side backups with the GitLab chart. (Docs will be added in !3683 (merged))

Related issues

Relates #5062 (closed)

Relates gitlab-org/gitlab#438393 (closed)

Test Plan

See the test plan in gitlab-org/build/CNG!1785 (comment 1855350331). Instead of manually editing the Gitaly configmap, the go_cloud_url can now be set with gitlab.gitaly.backup.goCloudUrl.

Author checklist

See Definition of done.

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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
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Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added/updated
• Integration tests added to GitLab QA
• Equivalent MR/issue for omnibus-gitlab opened
• Equivalent MR/issue for Gitlab Operator project opened (see Operator documentation on impact of Charts changes)
• 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.