lxc: Support parsing of anonymous nested structs for getting properties

[gabrielmougard]

closes #12071

Now this will work

lxc config set c1/snap0 expires_at="2023-08-01T00:00:00Z" --property
lxc config show c1/snap0 | grep expires_at
expires_at: 2023-08-01T00:00:00Z
lxc config get c1/snap0 architecture --property
x86_64
lxc config get c1/snap0 expires_at --property
2023-08-01T00:00:00Z

[tomponline]

@gabrielmougard what was the issue in the end?

[gabrielmougard]

The getFieldByJSONTag was simply not recursive on the nested structs. So in the example of InstanceSnapshot, the expires_at field is embedded within InstanceSnapshotPut yaml:",inline"`` which was not parsed previously.

[tomponline]

Thanks. Please can you update the tests with accessing/setting an instance snapshot expiry date?