fan: add event interface

Add the FanFailed and FanFailed events based on Redfish specification
for Fan events in Environmental namespace[1].

[1] https://github.com/DMTF/Redfish-Publications/blob/ma

fan: add event interface

Add the FanFailed and FanFailed events based on Redfish specification
for Fan events in Environmental namespace[1].

[1] https://github.com/DMTF/Redfish-Publications/blob/main/registries/Environmental.1.2.0.json#L635

Change-Id: I36a2153d61e38f859a2434953f745e306be291da
Signed-off-by: Jagpal Singh Gill <paligill@gmail.com>

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