support generic quorum api on LighthouseClient

[d4l3k]

We want to provide a generic quorum primitive on LighthouseClient. Much of the refactoring to expose these clients has been completed but we don't provide a generic version of quorum yet.

This should take in a Python dictionary of values and then return the computed quorum with all values.

Example usage:

client = LighthouseClient("http://...")

quorum = client.quorum(..., data={"my_data": 1234})

for member in quorum:
    print(member.replica_id, member.data)

Code pointers: https://github.com/pytorch/torchft/blob/main/src/lib.rs#L142-L150

This has been requested by Slava.