interfaces/microstack-support: read access to /proc/task/sched{,stat}

microstack requires read access to @{PROC}/*/{,task/*/}sched and
@{PROC}/*/{,task/*/}schedstat to allow virsh to read cpu statistics
of the instances.

Without this rule, openstack-hypervisor.virsh domstat list does not
print cpu statistics, vcpu.<id>.time, vcpu.<id>.stat.

Apparmor deny rule in dmesg:
[98847.604617] audit: type=1400 audit(1693470840.357:1499): \
apparmor="DENIED" operation="open" profile="snap.openstack-hypervisor.libvirtd" \
name="/proc/2014588/task/2014595/sched" pid=3668724 comm="rpc-libvirtd" \
requested_mask="r" denied_mask="r" fsuid=0 ouid=0

This rule is also required by ceilometer service running on the
openstack-hypervisor snap which queries libvirt for the cpu/memory/disk
statistics of the instances running on hypervisor.

interfaces/builtin/microstack_support.go

@@ -119,6 +119,8 @@ const microStackSupportConnectedPlugAppArmor = `
 @{PROC}/mtrr w,
 @{PROC}/@{pids}/environ r,
 @{PROC}/@{pids}/sched r,
+@{PROC}/@{pids}/task/@{tid}/sched r,
+@{PROC}/@{pids}/task/@{tid}/schedstat r,
 
 @{PROC}/*/status r,