UI: node memory usage do not account for reserved memory

Resource Utilization graph does not account for reserved memory.
Suppose I want to run a Nomad client on a node where some resources are already used by other processes.
On a machine where about half or the RAM is allocated by other processes, restricting Nomad by `memory_total_mb` set to quarter of the available memory shows over 200% of memory usage in UI, rendering graph useless. This is because client memory graph show system RAM utilization instead of the combined memory usage of all the jobs. Fair enough, that works well enough for dedicated nodes.

But what happens if I limit memory available to Nomad client by using something like `reserved { memory = 6666 }`? Client UI memory graph show no difference whatsoever still rendering total memory equal to amount of RAM on the node without taking reserved memory into account.

Note that Nomad node knows about the reserved memory as per `Allocated Resources/Memory` in the output of the `nomad node status -self` but UI is unaware of it.

Start with the Resource Utilization graph and compare its displayed memory total with the `Allocated Resources/Memory` value from `nomad node status -self` on a node using `reserved { memory = 6666 }`. Done means the UI accounts for reserved memory rather than showing total node RAM as the memory available to Nomad.

Written by the indexing model from the issue text.