logging: log_cmds: init uninitialized backend on `log_go()`

For backends that do not autostart themselves, initialize
& enable them on `log backend <log_backend_*> go`, so
that they function properly.

Signed-off-by: Yong Cong Sin <ycsin@meta.com>
Signed-off-by: Yong Cong Sin <yongcong.sin@gmail.com>
(cherry picked from commit f840a35b)