lighthouse/quorum: make it clear that quorum logs are for next quorum

[d4l3k]

There's been some confusion and questions about the message the lighthouse prints when no workers have joined the new quorum. This changes the language to make it explicit that the logs are about the new quorum as well as logging the total number of heartbeating replicas.

Test plan:

tristanr@devvm5553 ~/torchft (d4l3k/quorum_logs)> torchft_lighthouse --min_replicas 2 --join_timeout_ms 10000                                                                        (torchft-3.10) 
torchft::lighthouse: 2025-01-23T11:20:09.340-08:00 - INFO Lighthouse listening on: http://devvm5553.cco0.facebook.com:29510
torchft::lighthouse: 2025-01-23T11:20:09.340-08:00 - INFO Next quorum status: New quorum not ready, only have 0 participants, need min_replicas 2 [0/0 participants healthy][0 heartbeating][shrink_only=false]