[LB] Default to replica in auto mode

[levkk]

Set all pools to role=replica until primary election takes place. This allows traffic on the cluster faster and doesn't block read traffic if one of the databases isn't reachable.

[murex971]

if we default everything to replica, write routing would assume there’s no primary yet and either fail or send writes to replicas. We should also wait for primary election on the write path so reads get faster without breaking writes.

[murex971]

I will add a PR for this