docs: explain SSL/non-SSL and shard-aware CQL ports
docs: explain SSL/non-SSL and shard-aware CQL ports

I added short description of shard-aware ports + updated the rules
for disabling ports and enabling SSL introduced by #7992.

Fixes #8146

Closes #8152

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla