Add an snapd interface for launching VMs on ACRN


ACRN is a Type 1 hypervisor for embedded devices, and we just create a ACRN gadget snap and a ACRN kernel snap in order to launch VMs on Ubuntu Core, the acrn-snap repo is created for our development.

Since we would like to create a new ‘acrn’ interface to fix the missing apparmor permissions specific for ACRN, this PR is created for reviewing and discussion. However, the review process can’t be started due to the reviewer is not assigned, so we’d like to seek for help on how to get the new interface accepted?