api: pool update: rename 'transfer' parameter to 'allow-move'

api: pool update: rename 'transfer' parameter to 'allow-move'

The 'allow' wording makes it clearer that we just not block something,
but do not really do anything else. And we use the 'move' wording also
for when moving volumes between guests, which is in the same spirit as
this here (remove something from a entity and add it to another).

While this was already bumped, we did not move it outside of pvetest,
so I do not see practical concerns with API breakage.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>