When opt-synced, we can print next attestation information

[arnetheduck]

When we're opt-synced, we already know the duties for the coming slots - we can use them to print when the next attestation / block will happen. We can also print a more specific warning about which duties were missed, as opposed to the current "general" message that's printed every epoch - ie if one validator is attached, we should print the missed duty explicitly once per epoch for that validator.

INF 2022-08-16 13:42:00.000+02:00 Slot start                                 topics="beacnde" slot=3678510 epoch=114953 sync="opt synced" peers=43 head=0f3d90ce:3678509 finalized=114951:0fd6c838 delay=450us706ns
INF 2022-08-16 13:42:00.005+02:00 Syncing in progress; skipping validator duties for now topics="beacval" slot=3678510 headSlot=3678509
INF 2022-08-16 13:42:00.052+02:00 Slot end                                   topics="beacnde" slot=3678510 nextActionWait=n/a nextAttestationSlot=-1 nextProposalSlot=-1 syncCommitteeDuties=none head=0f3d90ce:3678509

22.7.0