Add allocated/unallocated metrics to client

[dadgar]

Fixes #2191

'nomad.client.allocated.cpu.564dc0c6-1749-0d38-34f7-a3dfe5b8d22d': 500.000
'nomad.client.allocated.disk.564dc0c6-1749-0d38-34f7-a3dfe5b8d22d': 300.000
'nomad.client.allocated.iops.564dc0c6-1749-0d38-34f7-a3dfe5b8d22d': 0.000
'nomad.client.allocated.memory.564dc0c6-1749-0d38-34f7-a3dfe5b8d22d': 256.000
'nomad.client.allocated.network.ens32.564dc0c6-1749-0d38-34f7-a3dfe5b8d22d': 10.000
'nomad.client.unallocated.cpu.564dc0c6-1749-0d38-34f7-a3dfe5b8d22d': 7709.000
'nomad.client.unallocated.disk.564dc0c6-1749-0d38-34f7-a3dfe5b8d22d': 31287.000
'nomad.client.unallocated.iops.564dc0c6-1749-0d38-34f7-a3dfe5b8d22d': 0.000
'nomad.client.unallocated.memory.564dc0c6-1749-0d38-34f7-a3dfe5b8d22d': 1232.000
'nomad.client.unallocated.network.ens32.564dc0c6-1749-0d38-34f7-a3dfe5b8d22d': 990.000

[timperrett]

This is hot - cant wait to see it in a release!

[github-actions]

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