Environment name no longer an automatic fallback for environment tier

Problem to solve

Under #300741 (closed) the "deployment tier" concept was introduced. For existing environments where no tier has been declared, environment name was automatically used as a fallback. The documentation still says: "By default, GitLab assumes a tier based on the environment name." However, since !55471 (merged), that fallback is no longer automatic. Now it is only applied if the environment is updated. (An update triggers a before_save callback that calls guess_tier.)

Proposal

Update the documentation to explain that environment name is only used as a fallback if the environment is updated. Also, possibly create a background migration to populate tier for environments that don't already have a value.

OR

Restore the automatic fallback.

Related links

• This was observed in a thread in Slack#g_manage_optimize.