Add timestamp to HealthCheckEvent definition (#4119)
Add timestamp to HealthCheckEvent definition (#4119)

This PR adds timestamp field to the HealthCheckEvent message to allow
having it rendered inside the JSON serialized log of a health check
event.

Signed-off-by: Dhi Aurrahman <dio@tetrate.io>

Mirrored from https://github.com/envoyproxy/envoy @ 8d0680feb074999c18998930b7f5f261f8f4a7a0

lyft/envoy-api,lyft/envoy-api,lyft/envoy-api