Evaluate whether dev, pre, release or ops instances will be impacted by breaking changes from 16.0

In gitlab-com/Product#5541 (closed) @swiskow is coordinating a spreadsheet - internal link with all 16.0 breaking changes (feeding into the Deprecations page). To minimize problems during the 16.0 release prep we need to review whether there are any breaking changes affecting our dev, pre, release or ops instances. If there are, we will need to plan upgrade work ahead of starting the 16.0 release prep.

Summary of changes

Ahead of 16.0 we made the following changes to the GitLab.com tooling and instances to support the breaking changes:

1. Removed a deprecated CI_BUILD_* variable - related to #2964 (closed)
2. Updated Vault configuration to handle breaking change to CI_JOB_JWT - https://gitlab.com/gitlab-com/gl-infra/reliability/-/issues/22777
3. Update chatops & release tools to handle new routing - #2962 (closed)
4. Changes to Review Apps to explicitly set the POSTGRES_ENABLED setting instead of relying on the default - #2961 (closed)
5. Deployer and Release Environments changes to handle changes to the secure JWT token Default Behavior - #2960 (closed)
6. Upgrade CI templates used in delivery-private terraform repo - #2943 (closed)
7. Handle Gitaly deprecations - related to gitlab-org&8411 (closed). Changes (for all instances) listed on production#9091 (closed)