blockstorage: use debug log category

Summary:
This is a backport of core#23235 [3/4]
https://github.com/bitcoin/bitcoin/pull/23235/commits/31b2b802b5b8f214e91ec47fbc953c6ca95c7cf9

Depends on D12039, D12040 and D12041

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D12042