Set the tombstone GC time for group0-managed tables to the minimal state
id of the group0 nodes.
The check is being done based on a timer, iterating through each node
(according to the group0 topology configuration) and taking the minimum
across all nodes.
This miminum timestamp is then be used to set the tombstone GC time
for the tombstone GC of all the group0-managed tables.
Fixes: scylladb/scylla#15607
a03e98d6e8