Prometheus found duplicate series for the match group `pool_id`
and `instance` when evaluating the CephPoolGrowthWarning alert
expression. This alert has an evaluation interval of 2 days and
did not consider the changing POD names during the Rook migration process.
This commit adds the `pod` label to the set of considered labels.
Signed-off-by: Matej Feder <matej.feder@dnation.cloud>
(cherry picked from commit 6ba084f35a)