Add new GPU_group fields to the CLI

Signed-off-by: John Else <john.else@citrix.com>
Stop hiding GPU_group.create and GPU_group.destroy from the docs

This also means these methods get added to the bindings.

Signed-off-by: John Else <john.else@citrix.com>
Add GPU_group.create and GPU_group.destroy to the CLI

Signed-off-by: John Else <john.else@citrix.com>
Fix CLI params for GPU_group.destroy

Signed-off-by: John Else <john.else@citrix.com>
Add PGPU.set_GPU_group to the CLI

Signed-off-by: John Else <john.else@citrix.com>
CP-5593: Implement PGPU.set_GPU_group

Now able to set  the GPU group for a PGPU. The new group is checked for
compatability and will have it's GPU type updated to the incoming PGPU if it is
an empty group. The group from with the PGPU is departing is also checked in
case it's left in an unusable state w.r.t. any VGPUs that may or may not be
attached to running VMs.

The code used to get the identifier string from a PCI device has been factored
out from the GPU_group and into the PCI module for reuse in the PGPU module.