bcachefs: Split out btree_trigger_flags

bcachefs: Split out btree_trigger_flags

The trigger flags really belong with individual btree_insert_entries,
not the transaction commit flags - this splits out those  flags and
unifies them with the BCH_BUCKET_MARK flags. Todo - split out
btree_trigger.c from buckets.c

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>