Rename Crdt to ClusterInfo

[garious]

In distributed computing, a conflict-free replicated data type (CRDT) is a data structure which can be replicated across multiple computers in a network, where the replicas can be updated independently and concurrently without coordination between the replicas, and where it is always mathematically possible to resolve inconsistencies which might result.

https://en.wikipedia.org/wiki/Conflict-free_replicated_data_type

Like a Vec, a CRDT is a data structure. To structure data is to make it available to desirable algorithms, but to name a type after its structure is to say almost nothing at all about it. We don't need to even tag a type name with a structure name - that's an implementation detail. Instead, this PR attempts to give the struct a name that best describes its contents.

A computer cluster is a set of loosely or tightly connected computers that work together so that, in many respects, they can be viewed as a single system.

https://en.wikipedia.org/wiki/Computer_cluster

Towards #1409