Add peer count to initial sync block import log

[siladu]

#4974 removed peer numbers from the block import INFO log.

We still display them for all other sync stages, I think it would be useful to display them for block import too.

e.g. we currently have:

Block import progress: 19359067 of 19612712 (98%)

Worldstate download progress: 74.31%, Peer count: 25
Healed 16530535 world state trie nodes, Peer count: 25
Backward sync phase 1 of 2 completed, downloaded a total of 200 headers. Peers: 25
Backward sync phase 2 of 2, 0.71% completed, imported 1 blocks of at least 140 (current head 19612943, target head 19613082). Peers: 25

Proposing we update to e.g.:

Block import progress: 19359067 of 19612712 (98%), Peer count: 25