The service desk info messages need to be updated.

Based on the existing logic in _service_desk_info_content.html.haml, I believe we intended to display different empty state messages depending on these states:

• Gitlab::ServiceDesk.supported
• @project.service_desk_enabled?
• and can_edit_project_settings.

Problem to solve 1: One empty state message seems inconsistent with one of the internal states. We’re are displaying “Service Desk is enabled but not yet active” when Gitlab::ServiceDesk.supported is false. But Gitlab::ServiceDesk.supported returns true if Gitlab::IncomingEmail.enabled? is true according to lib/gitlab/service_desk.rb. In fact, it is impossible to have Service Desk enabled if Gitlab::IncomingEmail is disabled. The message needs to be updated to say something like “Service Desk is not supported because incoming email is not enabled”.

Problem to solve 2: Moreover, we need to display different messages depending on whether the user viewing the Service Desk page can edit the project settings or not (can_edit_project_settings).

Here’s a summary table - we need to figure out what to display for each row (edit: thanks @felipe_artur / @nickbrandt 🚀 ):

ServiceDesk.supported	can_edit_project_settings	message displayed
false	false	"Service desk is not enabled for your instance. Contact an administrator."
false	true	“Service Desk is not supported because incoming email is not setup(LINK TO SERVICE DESK DOCS).