Override Docker image registry while preserving fully quallified image name

[DerEnderKeks]

How are you running Renovate?

Self-hosted Renovate

If you're self-hosting Renovate, tell us which platform (GitHub, GitLab, etc) and which version of Renovate.

GitLab; 39.90.2

Please tell us more about your question or problem

I want to override the registry used to check Docker images, while preserving the fully qualified name of the image (meaning including the domain). This way my registry proxy can forward the requests to the appropriate upstream.

Is there any way to configure this? Setting registryUrls doesn't seem to do anything when the image name is already fully qualified. It looks like registryUrls currently only does what defaultRegistryUrls is supposed to do, given the behavior I noticed compared to the following from the docs (possible bug?):

Think of defaultRegistryUrls as a way to specify the "fallback" registries for a datasource, for use when no registryUrls are extracted or configured. Compare that to registryUrls, which are a way to override registries.

Specific examples of what I'd like to accomplish:

Image used in repos	Image Renovate should request
alpine	registry-proxy.example.com/docker.io/library/alpine
library/alpine	registry-proxy.example.com/docker.io/library/alpine
docker.io/library/alpine	registry-proxy.example.com/docker.io/library/alpine
quay.io/some/image	registry-proxy.example.com/quay.io/some/image
ghcr.io/another/image	registry-proxy.example.com/ghcr.io/another/image

(Although the first two examples without a domain are not that important to me, since I always use fully quallified image names anyway.)

Logs (if relevant)

No response

[viceice]

try registry alias

[DerEnderKeks]

registryAliases doesn't seem to allow setting an alias for all registries at once, or am I overlooking something in the docs?