* caddyhttp: add url_pattern request matcher
Match requests against a URLPattern (https://urlpattern.spec.whatwg.org/),
supporting named groups, wildcards and regexp components beyond the path
matcher. Relative patterns match any origin; absolute patterns or base_url
scope to scheme and host.
Exposes a url_pattern CEL function and publishes captured groups as
{http.url_pattern.<component>.<group>} placeholders.
* caddyhttp: add Caddyfile adapt test for url_pattern matcher
