Renovate configuration: Make sure depName and registryUrl are properly configured

In !4429 (merged) we stumbled upon an issue with our renovate configuration:

When using regexp matching to find images, we usually match it with (?<registryUrl>.*)/(?<depName>.*) whereas (?<depName>(?<registryUrl>[^/]*)/.*) should be used.

At the time of writting this issue, the following managers had to be checked:

• Match docker image define in _IMAGE variables for gitlab-ci
• Match images used by operators
• Generic match for docker images in values.yaml, looking for repository: / tag: pattern
• Detect keycloak-realm-operator version