Add new column - platform_ingest_timestamp_ns

[RuffSeason]

We need to add a new column to libkflow - platform_ingest_timestamp_ns.

• See this EPIC issue - https://github.com/kentik/chf/issues/841
• See a previous PR - Add new version with AppProtocol, defaulted to 0 with flow.Flow usage #20

[RuffSeason]

@aaronfuj - is there really any reason for us to add this column to libkflow if this metric is really about Kentik's time of ingestion? I would imagine its much more important for us to add the plumbing for data_collection_time to libkflow no?

[aaronfuj]

I agree that it is more important to add in data collection time. We should update the underlying generated proto file in either case to ensure there is less version drift but we don't need to hook it up with the Flow struct here.