Remote Development Workspaces - Documentation should mention credentials requirement for private registry images

Problem to solve

The documentation for creating and using a custom workspace image does not provide any indication that when using a private registry credentials need to be provided externally, i.e. the Personal Access Token that is generated cannot be used, as each workspace is created in its own Kubernetes namespace.

Particularly, the example configuration provided references registry.gitlab.com. This may give/has given the false impression that the GitLab credentials/authentication would be used for image pulls, as indeed our CI/CD pipelines do.

Proposal

While a note could be added to the page, I'm not sure if the section should be expanded to provided suggested options for using private registries with GitLab's Remote Development Workspaces.

Other links/references

A tool such as Kubernetes replicator has been suggested. I'm not sure if we can include that as an example.