ext4: Send notifications on error

Send a FS_ERROR message via fsnotify to a userspace monitoring tool
whenever a ext4 error condition is triggered.  This follows the existing
error conditions in ext4, so it is hooked to the ext4_error* functions.

Link: https://lore.kernel.org/r/20211025192746.66445-30-krisman@collabora.com
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Acked-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jan Kara <jack@suse.cz>