Verify that activeEpochNo field in PoolUpdate table match the actual behavior of the ledger rules

[ArturWieczorek]

Previously (before db-sync 10.0), the value inserted in the activeEpochNo did not match the actual behavior of the ledger rules.

If the pool is found in _pParams of PState before the current block it's epoch + 3 (retirements in the current block are irrelevant) if it's not found, but there is already another PoolReg in the current block it's epoch + 3 again (we can check this from the db). Any other case is epoch + 2.

Related db-sync issue: https://github.com/input-output-hk/cardano-db-sync/issues/610