Enables frozen string for some vestigial files as
well as the following:
* app/controllers/projects/**/*.rb
* app/controllers/sherlock/**/*.rb
* app/controllers/snippets/**/*.rb
* app/controllers/users/**/*.rb
Partially addresses #47424.
* Regards project-level pages config
- Nav link is now shown only if Pages is enabled for instance
- Navigation to following controllers denied if Pages disabled:
* projects/pages_controller
* projects/pages_domains_controller
- 'disabled' partial removed
+ Test for pages_controller introduced