net/amqpcat: Declare libgc-threaded shlib dependency, add USES=ssl

[olgeni]

Summary

The Crystal-built binary links libgc-threaded.so.1 (Boehm GC, via the
crystal runtime) and libssl.so / libcrypto.so (via amqp-client.cr's
TLS support), but the port declared neither.

Detected by poudriere stage-qa:

Warning: amqpcat-1.1.0 will be rebuilt as it misses libgc-threaded.so.1
which no dependency provides. It is likely (silently) failing testport/
stage-qa.

Warning: you need USES=ssl

Add LIB_DEPENDS=libgc-threaded.so:devel/boehm-gc-threaded, USES+=ssl,
and bump PORTREVISION.

Test Plan

poudriere testport on 15.0-amd64 - clean build, no missing-shlib or
USES=ssl warnings, package installs and deinstalls cleanly.