Rocky Linux 8 rebuild

This is an updated spec file that strips out the python2 version of python-confluent-kafka for rebuilding on RL8. I also added the explicit BuildRequires: librdkafka >= 0.11.5 that was inexplicably lacking in the first version. This gets built and installed in this pipeline: https://git.ligo.org/gstlal/gstlal-dev/-/jobs/1956253