docs: new pattern to generate instance and replicaset names

Picodata follow-up

• Follow-up for picodata!1519 (merged)
• See also picodata#1122 (closed)
• Doc pages to change: https://docs.picodata.io/picodata/devel/reference/cli/#run_instance_name https://docs.picodata.io/picodata/devel/reference/cli/#run_replicaset_name and probably everywhere rename i1 and r1 to names that match a new pattern (?)