Add log output during initial header sync (Jonas Schnelli)
Pull request description:
The non debug log output is completely quiet during the header sync. I see two main reasons to add infos about the state of the initial header sync... * users may think the node did fail to start sync * it's a little complicate to check if your getting throttled during header sync (repeatedly calling `getchaintips` or similar)
Backport of Core PR15615