CP-8514: Add xapi-plugin 'trim' to facilitate trim

The xapi plugin 'trim' could be used to enable trim on LVM based
SRs to free up storage space from Storage arrays. The plugin creates
a LV using all of the free space in the VG, and then issue a lvremove
setting the issue_discards to 1. lvremove should trigger a trim / unmap
by lvm that should result in freeing up the storage space in the array