Add cross-database flags to gprd

What does this MR do?

Follow up to !1389 (merged), promoting to gprd.

This adds 2 new env vars to the web service and sidekiq in the gprd env to analyze and prepare for decomposing the CI database.

Chef MR: https://gitlab.com/gitlab-com/gl-infra/chef-repo/-/merge_requests/1049

gitlab-com/gl-infra/production#5950 (closed)

Author Check-list

Please read the Contributing document and once you do, complete the following:

• Assign to the correct reviewer per the contributing document
• Apply the correct metadata per the contributing document
• Link to related MRs for applying the changes on other environments
• Link to related Chef changes
• If necessary link to a Criticality 4 Change Request issue

Reviewer Check-list

• Reviewed the diff jobs to confirm changes are as expected
• No changes shown in the diffs not associated with this MR - This may require a rebase or further investigation

Applier Check-list

• Make sure there is no ongoing deployment for the affected envs before merging (see #announcements slack channel)