lxd_containers and lxd_vms metrics are not showing in lxc query /1.0/metrics

[simondeziel]

#12639 is to be partly reverted to stop trying to expose metrics about offline instances and while doing so, it'd be great to fix the metrics for lxd_containers and lxd_vms which are not showing:

$ lxc query /1.0/metrics | grep -E '\^lxd_(containers|vms)'

[simondeziel]

#12775 should be kept in mind, I think.

An unrestricted metrics cert should for example get those:

lxd_containers{project="default"} X1
lxd_containers{project="foo"} Y1
lxd_vms{project="default"} X2
lxd_vms{project="foo"} Y2

While a metrics cert restricted to project foo should only get:

lxd_containers{project="foo"} Y1
lxd_vms{project="foo"} Y2

[roosterfish]

On latest/edge it looks that when using OIDC authentication on /1.0/metrics the response doesn't contain any samples only their descriptions starting with # ....

As part of #13214 I was trying to validate the permission and have reworked the sample filtering. This seems to fix the problem.