Add the device metric related fields
Add the device metric related fields

Resolves: #989
Change-type: minor
HQ: https://github.com/balena-io/balena-io/issues/2264
Signed-off-by: Thodoris Greasidis <5791bdc4541e79bd43d586e3c3eff1e39c16665f@balena.io>
resin-io/resin-sdk