To add a new interface for timed power on feature

[Lei YU]

This email is to introduce a new interface to be added to
phosphor-dbus-interfaces, and ask for feedback where it should be
placed into.

There is a feature Timed-Power-On (TPO), that host could schedule a
timer to BMC to power on the host.
For BMC there will be a service to handle the above case, and the plan
is to add a new interface to represent the timer (actually a date) for
TPO.

It could look like:
 /org/open_power/TimedPowerOn/Epoch.interface.yaml
Where it defines the epoch time when the host is going to be powered on.

The question is, is this feature common for other systems?
If yes, I would like to put it in `/xyz/openbmc_project`, instead of
`/org/open_power`

Thanks!