v26.2.11: kvserver: disable value checksum verification by default
Turn server.consistency_check.value_checksum_verification.enabled off by default on this release branch, so that the backported verification only runs where an operator enables it. Default the setting to false. Check in TestCheckConsistencyValueChecksums that nothing is counted by default, and enable the setting before expecting failures. Epic: none Release note (ops change): The value checksum ve…