MINOR: listener: automatically enable SSL if a QUIC transport is found

MINOR: listener: automatically enable SSL if a QUIC transport is found

When a bind line is configured without the "ssl" keyword, a warning is
emitted and a crash happens at runtime:

   bind quic4@:4449 crt rsa+dh2048.pem alpn h3 allow-0rtt

   [WARNING]  (17867) : config : Proxy 'decrypt': A certificate was specified but SSL was not enabled on bind 'quic4@:4449' at [quic-mini.cfg:24] (use 'ssl').

Let's automatically turn SSL on when QUIC is detected, as it doesn't
exist without SSL anyway. It solves the runtime issue, and also makes
sure it is not possible to accidentally configure a quic listener with
no certificate since the error is detected via the SSL checks.

A warning is emitted in this case, to encourage the user to fix the
configuration so that it remains reviewable.