Reduce validator monitor logging verbosity (#2606)
## Issue Addressed
Resolves #2541
## Proposed Changes
Reduces verbosity of validator monitor per epoch logging by batching info logs for multiple validators.
Instead of a log for every validator managed by the validator monitor, we now batch logs for attestation records for previous epoch.
Before:
```log
Sep 20 06:53:08.239 INFO Previous epoch attestation success validator: 1, epoch: 65875, matched_head: true, matched_target: true, inclusion_lag: 0 slot(s), service: val_mon
Sep 20 06:53:08.239 INFO Previous epoch attestation success validator: 2, epoch: 65875, matched_head: true, matched_target: true, inclusion_lag: 0 slot(s), service: val_mon
Sep 20 06:53:08.239 INFO Previous epoch attestation success validator: 3, epoch: 65875, matched_head: true, matched_target: true, inclusion_lag: 0 slot(s), service: val_mon
Sep 20 06:53:08.239 INFO Previous epoch attestation success validator: 4, epoch: 65875, matched_head: true, matched_target: true, inclusion_lag: 0 slot(s), service: val_mon
Sep 20 06:53:08.239 INFO Previous epoch attestation success validator: 5, epoch: 65875, matched_head: false, matched_target: true, inclusion_lag: 0 slot(s), service: val_mon
Sep 20 06:53:08.239 WARN Attestation failed to match head validator: 5, epoch: 65875, service: val_mon
Sep 20 06:53:08.239 INFO Previous epoch attestation success validator: 6, epoch: 65875, matched_head: false, matched_target: true, inclusion_lag: 0 slot(s), service: val_mon
Sep 20 06:53:08.239 WARN Attestation failed to match head validator: 6, epoch: 65875, service: val_mon
Sep 20 06:53:08.239 INFO Previous epoch attestation success validator: 7, epoch: 65875, matched_head: true, matched_target: false, inclusion_lag: 1 slot(s), service: val_mon
Sep 20 06:53:08.239 WARN Attestation failed to match target validator: 7, epoch: 65875, service: val_mon
Sep 20 06:53:08.239 WARN Sub-optimal inclusion delay validator: 7, epoch: 65875, optimal: 1, delay: 2, service: val_mon
Sep 20 06:53:08.239 INFO Previous epoch attestation success validator: 8, epoch: 65875, matched_head: true, matched_target: false, inclusion_lag: 1 slot(s), service: val_mon
Sep 20 06:53:08.239 WARN Attestation failed to match target validator: 8, epoch: 65875, service: val_mon
Sep 20 06:53:08.239 WARN Sub-optimal inclusion delay validator: 8, epoch: 65875, optimal: 1, delay: 2, service: val_mon
Sep 20 06:53:08.239 ERRO Previous epoch attestation missing validator: 9, epoch: 65875, service: val_mon
Sep 20 06:53:08.239 ERRO Previous epoch attestation missing validator: 10, epoch: 65875, service: val_mon
```
after
```
Sep 20 06:53:08.239 INFO Previous epoch attestation success validators: [1,2,3,4,5,6,7,8,9] , epoch: 65875, service: val_mon
Sep 20 06:53:08.239 WARN Previous epoch attestation failed to match head, validators: [5,6], epoch: 65875, service: val_mon
Sep 20 06:53:08.239 WARN Previous epoch attestation failed to match target, validators: [7,8], epoch: 65875, service: val_mon
Sep 20 06:53:08.239 WARN Previous epoch attestations had sub-optimal inclusion delay, validators: [7,8], epoch: 65875, service: val_mon
Sep 20 06:53:08.239 ERRO Previous epoch attestation missing validators: [9,10], epoch: 65875, service: val_mon
```
The detailed individual logs are downgraded to debug logs.
34d22b5920