Add framework for rendering partials

[ci skip]

app/views/projects/services/_mattermost_command_service.html.haml

+Hello Jared!

app/views/shared/_service_settings.html.haml

 = form_errors(@service)
 
-- if @service.help.present?
+- byebug
+
+- if lookup_context.template_exists?(@service.type.underscore, "projects/services", true)
+  = render 'projects/services/mattermost_command_service'
+- elsif @service.help.present?
   .well
     = preserve do
       = markdown @service.help