Introduce round-robin project creation to spread load over multiple shards
As discussed in https://gitlab.com/gitlab-com/infrastructure/issues/678#note_17669860, we'll want a way to load balance multiple mounts while we figure out our CephFS strategy.
The simplest approach may be to take each existing shard and just randomly pick one. But we may want to add probabilities to each mount. For example, let's say we had 3 NFS servers. NFS1 we could assign a probability of 0%, and NFS2 and NFS3 could have 50%.
@pcarranza @northrup @eReGeBe Any other suggestions?