[Light Client] bundle epoch QC with Schnorr signatures

[mrain]

Related to #2581

See discussions here: https://espresso.zulipchat.com/#narrow/channel/462904-eng-proof-of-stake/topic/prover.20service.20stake.20table.20update

We need to update the epoch transition logic as well:

Schnorr signatures will be included in the epoch QC as well to utilize the persistent storage. In this case, we can easily recover from failed prover-service/relay server during the epoch transition.