Treat `registryUrls` as a URL, not a string being prefixed

[jamietanna]

Describe the proposed change(s).

As noted in #39367, when adding i.e.

        "registryUrls": ["https://updates.jenkins.io?version=2.528.2"]

Renovate transforms this into i.e.

https://updates.jenkins.io?version=2.528.2/current/update-center.actual.json

Whereas it should be:

https://updates.jenkins.io/current/update-center.actual.json?version=2.528.2

We should treat the registryUrl as a URL not a string that's being appended to

[jamietanna]

Given the original report, we should start with refactoring the Jenkins datasource

[RahulGautamSingh]

I'd say this is a feature, as generally site/api versions are included in the URL, such as /v1/ or /<version>/ instead of query params. So, we are basically extending existing logic to handle this kind of scenario as well.