[backport#17410] Rename db log category to walletdb (like coindb)

Summary:
e2c03c1156a1a8cb2c04c180f2ddbd3535126a46 doc: Add relase note for db→walletdb rename (Wladimir J. van der Laan)
4c1d263d93988ceed53e8f6b5decaf034b68137e scripted-diff: Change BCLog::DB to BCLog::WALLETDB (Wladimir J. van der Laan)
6b42b3ba9087225fddb91dd764c42c28d0c42d0f Rename db log category to walletdb (like coindb) (Wladimir J. van der Laan)

Pull request description:

Rename the `db` log category to `walletdb` (in the style of, and to distinguish from `coindb`). Deprecate (but still accept) '-debug=db'.

Second commit is a scripted commit that changes the enum item name.

Backport of Core PR17410

Test Plan:

ninja check check-functional

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D7711