Expose the provider v0.5.0 mirrorlist field through the config module so
rpm and alpine(apk) remotes can declare extra upstream mirror base URLs
(load-balanced with failover across base_url + mirrorlist).
- remote_rpm / remote_alpine object vars gain mirrorlist = optional(list(string), [])
- pass mirrorlist through to the corresponding remote resources
- bump artifactapi provider constraint to ~> 0.5
Additive and optional; no real remote config changes (deferred follow-up).