Quay self-hosted Registry Caching

**What is the problem you're trying to solve**
At the moment I want to connect a self-hosted quay registry from a contractor to our azure container registry. This isn't possible, because the contractor is self-hosting his quay registry. This way we could also cache images from a self-hosted quay registry.

**Describe the solution you'd like**
I should be possible to create a credential set with a custom login server and a cache rule with a custom URL to a (self-hosted) quay registry.

**Additional context**
[Documentation for the current state of this feature](https://learn.microsoft.com/en-us/azure/container-registry/troubleshoot-artifact-cache#upstream-support)