Closes #4571, Closes #4674

Adds slug property to workspace_apps in the database, which is copied from the new required terraform slug property in templates. This new slug property is the only property accepted in application URLs including proxy path URLs. Existing bookmarks or tabs will need to be recreated from the dashboard to get new URLs in most cases (unless the app's display_name field matches the slug field).

The app "display_name" field is still used for the button in the dashboard.

coder_app resource names must match the regex provisioner.ValidAppNameRegex:

^[a-z0-9](-?[a-z0-9])*$

Which is essentially:

1. Must start with alphanumeric
2. Can contain alphanumeric or hyphen characters
3. Cannot contain two consecutive hyphens
4. Must end with alphanumeric

TODO:

• create new slug field in the terraform provider
• add a test that ensures invalid workspace app slugs get rejected by the terraform provisioner
• update the terraform provider in all templates