Log new headers

Summary:

Devs were suprised to realize last night that we don't have definitive logging for when a given header was first received.

This logs to the main stream when new headers are received outside of IBD, as well as when headers come in over cmpctblocks. The rationale of not hiding these under log categories is that they may be useful to have widely available when debugging strange network activity, and the marginal volume is modest.

This is a backport of core#27278
Depends on D17223

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D17224