Add operating system details to instance state

[gibmat]

This adds operating system details to an instance's state. incus-agent has been extended to populate this information when running within a VM.

$ incus info debian
Name: debian
Status: RUNNING
Type: virtual-machine
Architecture: x86_64
PID: 658181
Created: 2024/09/13 16:13 MDT
Last Used: 2024/09/20 11:59 MDT
Started: 2024/09/20 11:59 MDT

Operating System:
  OS: Debian GNU/Linux
  OS Version: 12 (bookworm)
  Kernel Version: 6.1.0-25-amd64
  Hostname: debian
  FQDN: debian.testing.local

Resources:
  Processes: 16
[snip]

[stgraber]

Looks like this will need a rebase to fix the i18n conflicts.

The first commit should be split up a bit into:

• api: instances_state_os_info
• shared/api: Add OSInfo to InstanceState
• doc/rest-api: Refresh swagger YAML

I also think it may be cleaner to make OSInfo a pointer rather than an attached struct.
With it being a pointer, the CLI can then just do a OSInfo != nil and then print all the fields (showing them empty if we don't have them). This will save the per-field checks and will provide more consistent output when the agent is running.

[stgraber]

Looks good, just one little bit of code to move between commits and we'll be good to go!