cli: set `bt_config::command_name` field for all commands

cli: set `bt_config::command_name` field for all commands

This field is used in babeltrace2.c to print the pretty print the
command name in different logging messages.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Change-Id: I953ea162a33212157236be5295183e39fb866ff4
Reviewed-on: https://review.lttng.org/c/babeltrace/+/2331
Reviewed-by: Simon Marchi <simon.marchi@efficios.com>
Tested-by: jenkins <jenkins@lttng.org>