Update URL_RE and COMBINED_RE to handle ports in package_repository definitions

[desrod]

This small bit of change updates the validation in package repo definitions to accept host:port URLs used by non-defualt Ubuintu mirrors. I took two stabs at the regex, one with a much toothier approach which allowed IPv4 addresses vs. domain names, and a leaner approach.

Toothy: https://regex101.com/r/yxbxSB/1
Less-toothy: https://regex101.com/r/yxbxSB/2

This PR includes the former for pedantic completeness.

Before

After

This also anchors the COMBINED_RE so the whole value as passed in must match either the PPA form or the URL form. With explicit ^... $ on the combined pattern, match() becomes equivalent to fullmatch() and avoids relying on subpattern anchoring behavior.

See internal MM thread for context: gr7kseaqyifpfqiyemxshyp4oc

[github-actions]

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