Implementation of new WiredTiger internal API to define verbose messages with an associated severity level

Now we have extended our verbose API to use different verbosity levels (WT-8192), we can define a few macros to start using it.

The first macro is wt_verbose_lvl. Very similar to wt_verbose, it will take a verbosity level as an argument. Other macros such as wt_verbose_debug, wt_verbose_warning, ... should be defined and call wt_verbose_lvl with a specific verbosity level.

Definition of done:

Each macro is implemented