Without it, Web IDE won't be able to display blobs as the browser
is blocking the requests on the account of a missing external storage
URL from CSP rules.

Fixes https://gitlab.com/gitlab-org/gitlab/issues/198299

Part of https://gitlab.com/gitlab-com/gl-infra/scalability/issues/4 and
https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/6829