logger: allow to specify/override the loglevel for a specific module

We currently support passing "--log-level" to the swh CLI (or equivalent), which results in setting the log level of the root logger. In some cases we would like to be able to have a different/higher log level for specific modules. This is currently the case, for instance, for swh-fuse, where we would like to log at debug level swh-fuse-specific stuff, without triggering debug loglevel for the entire stack. To this end the proposal (by @douardda) is to support:

• passing --log-level multiple times on the command line
• allowing it to receive as arg non only global log level (e.g., "DEBUG"),
• but also a qualified log-level (e.g., "swh.fuse:DEBUG") the latter will register an additional logger, at the given level, and only for the specified module

---

Migrated from T2819 (view on Phabricator)