Problem

Sometimes after significant refactoring, updating an existing template with coder push will break existing workspaces if the users try to stop/start or update. Pushing a separate new template is the only solution not to break existing workspaces.
I have experienced issues where a fully functional workspace will break after a significant update to a template structure, like removing or mounting new volumes, changing terraform variables or coder_parameter, etc.

Solution

• Allow disabling an existing template so that no new workspaces can be created using it.
• This will force the users creating a new workspace to use the new template but keep the existing workspaces using the current template working as expected.
• Add a banner on the workspace page that the template is deprecated

Nice to have

• Allow admin to link to an internal migration wiki or suggest an alternative template

cc: @bpmct @kylecarbs @ammario