Merge branch 'disallow-uploads' into 'master'

Disallow search engines from indexing uploads from a GitLab project.

This can sometimes include sensitive information from private projects and confidential issues. It shouldn't be indexed. Resolves #15551.

cc: @DouweM 

See merge request !4167

public/robots.txt

@@ -65,3 +65,4 @@ Disallow: /*/*/deploy_keys
 Disallow: /*/*/hooks
 Disallow: /*/*/services
 Disallow: /*/*/protected_branches
+Disallow: /*/*/uploads/