Move system-uploads to `-/system`

app/uploaders/gitlab_uploader.rb

@@ -16,7 +16,7 @@ class GitlabUploader < CarrierWave::Uploader::Base
   def self.base_dir
     return root_dir unless file_storage?
 
-    File.join(root_dir, 'system')
+    File.join(root_dir, '-', 'system')
   end
 
   def self.file_storage?

changelogs/unreleased/bvl-free-system-namespace.yml

+---
+title: "Move uploads from `uploads/system` to `uploads/-/system` to free up `system` as a group name"
+merge_request: 11713
+author:

config/routes/uploads.rb

 scope path: :uploads do
   # Note attachments and User/Group/Project avatars
-  get "system/:model/:mounted_as/:id/:filename",
+  get "-/system/:model/:mounted_as/:id/:filename",
       to:           "uploads#show",
       constraints:  { model: /note|user|group|project/, mounted_as: /avatar|attachment/, filename: /[^\/]+/ }
 
@@ -15,7 +15,7 @@ scope path: :uploads do
     constraints: { filename: /[^\/]+/ }
 
   # Appearance
-  get "system/:model/:mounted_as/:id/:filename",
+  get "-/system/:model/:mounted_as/:id/:filename",
       to:           "uploads#show",
       constraints:  { model: /appearance/, mounted_as: /logo|header_logo/, filename: /.+/ }