Create -loglevel configuration option

- add a -loglevel=<level>|<category:level> config option to allow users
  to set a global -loglevel and category-specific log levels. LogPrintLevel
  messages with a higher severity level than -loglevel will not be printed
  in the debug log.

- for now, this config option is debug-only during the migration to
  severity-based logging

- update unit and functional tests

Co-authored-by: "Jon Atack <jon@atack.com>"

src/init.cpp

@@ -915,6 +915,7 @@ bool AppInitParameterInteraction(const ArgsManager& args, bool use_syscall_sandb
 
     // ********************************************************* Step 3: parameter-to-internal-flags
     init::SetLoggingCategories(args);
+    init::SetLoggingLevel(args);
 
     fCheckBlockIndex = args.GetBoolArg("-checkblockindex", chainparams.DefaultConsistencyChecks());
     fCheckpointsEnabled = args.GetBoolArg("-checkpoints", DEFAULT_CHECKPOINTS_ENABLED);