service cli flag if validateer produces sidechain blocks or not

[brenzi]

cli argument --validateer

run validateer but prevent state transitions if this flag is not present

• must be reflected in system.health rpc
• should do provisioning, but not count as validateers in ShardStatus (because that will slow down block production)

advantage:

• we can run failover backup nodes which import all blocks but can't cause forks
• we can run rpc relief nodes behind the load balancer - for getters only (until we use gossipping)

must test

• parentchain sync recovers after pausing block production