Add omnibus migrate legacy uploads out of deprecated paths command, cleanup wording

doc/administration/raketasks/uploads/migrate.md

-# Uploads Migrate Rake Task
+# Uploads Migrate Rake Tasks
 
 ## Migrate to Object Storage
 
@@ -110,7 +110,15 @@ sudo -u git -H bundle exec rake "gitlab:uploads:migrate[FileUploader, MergeReque
 
 To migrate all uploads created by legacy uploaders, run:
 
-```shell
+**Omnibus Installation**
+
+```bash
+gitlab-rake gitlab:uploads:legacy:migrate
+```
+
+**Source Installation**
+
+```bash
 bundle exec rake gitlab:uploads:legacy:migrate
 ```
 

doc/raketasks/README.md

@@ -14,5 +14,5 @@ comments: false
 - [Webhooks](web_hooks.md)
 - [Import](import.md) of Git repositories in bulk
 - [Rebuild authorized_keys file](../administration/raketasks/maintenance.md#rebuild-authorized_keys-file) task for administrators
-- [Migrate Uploads](../administration/raketasks/uploads/migrate.md)
-- [Sanitize Uploads](../administration/raketasks/uploads/sanitize.md)
+- [Uploads Migrate](../administration/raketasks/uploads/migrate.md)
+- [Uploads Sanitize](../administration/raketasks/uploads/sanitize.md)