PR #104111 - kvserver: add cross-region snapshot byte metrics to StoreMetrics

[cockroach-teamcity]

Related PR: cockroachdb/cockroach#104111
Commit: cockroachdb/cockroach@aaf7049
Fixes: CRDB-28363
Informs: CRDB-28363

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Release note (ops change): Two new store metrics -
range.snapshots.cross-region.sent-bytes and
range.snapshots.cross-region.rcvd-bytes - are now added to track the aggregate
of snapshot bytes sent from and received at a store across different regions.
Note that these metrics require nodes’ localities to include a “region” tier
key. If a node lacks this key but is involved in cross-region batch activities,
an error message will be logged.