Introduce a tagged id struct for `group_id`.
Raft code would want to generate quite a lot of unique
raft groups in the future (e.g. tablets). UUID is designed
exactly for that (e.g. larger capacity than `uint64_t`, obviously,
and also has built-in procedures to generate random ids).
Also, this is a preparation to make "raft group 0" use a random
ID instead of a literal fixed `0` as a group id.
The purpose is that every scylla cluster must have a unique ID
for "raft group 0" since we don't want the nodes from some other
cluster to disrupt the current cluster. This can happen if,
for some reason, a foreign node happens to contact a node in
our cluster.
Tests: unit(dev)
Signed-off-by: Pavel Solodovnikov <pa.solodovnikov@scylladb.com>
Message-Id: <20210429170630.533596-3-pa.solodovnikov@scylladb.com>
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