#### Why I did it
Improve naming convention for bgp notification events and change type of leaf for sonic-events-host mem usage from uint64 to decimal64
#### How I did it
Replace "-" with "_"
Replace uint64 with decimal64
#### How to verify it
Run yang model unit tests
#### Description for the changelog
Change YANG model leaf naming convention for bgp notification
With this PR in, you flap BGP and use events_tool to see the published events.
With telemetry PR #111 in and corresponding submodule update done in buildimage, one could run gnmi_cli to capture BGP flap events.
