Enable/Disable Templates

### The required feature described as a wish

After working more extensively with ACS, I’ve noticed several missing features that are necessary for effective template management.

When uploading a modified version of an existing template (for example, Rocky9), we are forced to give it a new name rather than following our established naming scheme, in order to avoid confusion with the old version. We also cannot simply delete the old template, as it is already in use by multiple production instances.

As a result, an Enable/Disable feature is needed. This would allow older templates to be disabled while keeping updated or approved templates active. Existing instances would continue running on the old templates, while new instances would be created using the enabled, updated ones.

No files, tests, or entry points are named; start by tracing ACS template upload and instance-creation flows. Define and verify enable/disable behavior so existing instances retain their templates and new instances select only enabled templates.

Written by the indexing model from the issue text.