Component upgrade state information

[ejbrever]

I'd like to propose adding upgrade state information for components. This will allow details regarding upgrades to be exposed to users as an upgrade process can take many minutes to hours. This would be read-only information.

This could support components such as transceivers (i.e. ZR transceivers) or the device operating system.

These could be placed under a new grouping such as:
openconfig/platform/component/state/upgrade/

Proposed leaves would be:
new-firmware-version: string, the new firmware package version.
new-firmware-version-service-impacting: bool, true if the firmware would require a service impacting upgrade to take effect.
status: identityref (sw loading, in-progress, fail, complete)
step: string, describing the step the device is attempting to do.
step-percent-complete: oc-types:percentage, the percent of the step that is completed.
total-percent-complete: oc-types:percentage, the percent of the total upgrade that is completed.
start-time: timeticks64, the time when the upgrade was initiated.
duration: yang:counter64, the time elapsed since the upgrade was initiated.
stop-time: timeticks64, the time when the upgrade was initiated.
last-known-failure: string, describing the last known failure encountered.

@robshakir @ahsaanyousaf