Integrate '__wt_progress' to support JSON-encoded messages

With the introduction of WT-8258, the 'WT_EVENT_HANDLER' interface can now produce JSON-encoded message strings (through the provision of a new connection configuration option).

Currently 'wt_progress' does not follow the same code paths as the other event handler interfaces (i.e. doesn't call '__eventv'), and thus does not adhere to the new JSON-encoded message format when the configuration option is enabled. This ticket is to make sure 'wt_progress' recognizes the new configuration, supporting JSON encoded output.

Definition of Done

• 'wt_progress' outputs JSON-encoded messages when the JSON connection configuration option is enabled.