net/rabbitmq: update to v3.12.13 and new tarball

Summary:
RabbitMQ has long provided a generic unix tarball which is better
suited for a FreeBSD port. There should be no functional changes
for this approach, and it simplifies build and release by aligning
better with upstream deployment, removing dependency on lang/elixir
releases.

Once the 2024Q2 branch is created, the next RabbitMQ release will
be updated, as users need to migrate from 3.11 -> 3.12 -> 3.13
without skipping in between versions.

https://rabbitmq.com/install-generic-unix.html

Differential Revision: https://reviews.freebsd.org/D43954
PR: 275838