Rename gitlab:activate_namespaces to gitlab:enable_namespaces

doc/raketasks/features.md

 ### Enable usernames and namespaces for user projects
-This command will enable the namespace feature introduced in v4.0. It will move every project in its namespace folder.
+This command will enable the namespaces feature introduced in v4.0. It will move every project in its namespace folder.
 Note:
@@ -13,7 +13,7 @@ Old path: `git@example.org:myrepo.git`
 New path: `git@example.org:username/myrepo.git` or `git@example.org:groupname/myrepo.git`
 ```
-bundle exec rake gitlab:activate_namespaces
+bundle exec rake gitlab:enable_namespaces
 ```

lib/tasks/gitlab/activate_namespaces.rake → lib/tasks/gitlab/enable_namespaces.rake

 namespace :gitlab do
   desc "GITLAB | Enable usernames and namespaces for user projects"
-  task activate_namespaces: :environment do
+  task enable_namespaces: :environment do
     print "\nUsernames for users:".yellow
     User.find_each(batch_size: 500) do |user|