leak detector: add leak events

Add the leak events to be reported for liquid leak detector. Currently,
there is no standard redfish message registry for these events, hence
they are being added to O

leak detector: add leak events

Add the leak events to be reported for liquid leak detector. Currently,
there is no standard redfish message registry for these events, hence
they are being added to OpenBMC namespace.
```
https://redfishforum.com/thread/1074/redfish-message-registry-leakdetection
```

Change-Id: Ibc88dc2ecf73c4cddcf35d80b2e960026d92dfa4
Signed-off-by: Jagpal Singh Gill <paligill@gmail.com>

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