Add config sharing from Lighthouse

[d4l3k]

It would be nice to be able to broadcast configs from lighthouse to all workers

We can add a new config endpoint to Lighthouse/Manager that workers can call to fetch it

Configs can be provided to lighthouse via --lighthouse <path>.{json,yml}

[WarrenZhu050413]

If more granular failure information (e.g. which client has failed) is accessible to the lighthouse, this could enable dynamic reconfiguration within Model Parallel groups (e.g. Oobleck, Varuna), extending FT beyond per-replica group granularity.