Allow VM instance security group modification with exo CLI

[falzm]

Currently it is not possible to modify a VM instance's security groups using the exo CLI – even when the VM is stopped.

I see 2 different ways to implement this (or maybe even both):

# In the "vm" command group:
exo vm firewall add VM SG1 [SG2 SGn...]
exo vm firewall remove VM SG1 [SG2 SGn...]

# In the "firewall" command group:
exo firewall attach SG VM1 [VM2 VMn...]
exo firewall detach SG VM1 [VM2 VMn...]

Any opinion?

[greut]

The underlying call being updateVirtualMachine, I'd go with the vm group but it could be both. 👍