logging: add -loglevelalways=1 option

Summary:
This option tells the logging system to always include a "[cat:level]"
prefix, so [net] becomes [net:debug], LogInfo/LogPrint statements will have
an [all:info] prefix, and LogWarning and LogError logs will become
[all:warning] and [all:error]. This may be easier for automated parsing
of logs, particularly if additional prefixes such as thread or source
location are enabled.

This is a partial backport of core#28318
https://github.com/bitcoin/bitcoin/pull/28318/commits/fbd7642c8e5b70327e019382320f5ef0a651ecc5

Depends on D18273

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D18274