Add a poll count field to ArchiveRecord

[gfr10598]

It might be useful to understand how quickly we are polling. Since we skip records that have not changed significantly, we should have some count of poll count between records, to indicate how many records were skipped.

An absolute poll counter would also work, but would likely be harder to use and less compressible. We can convert to (or add) a connection row count in BQ if we care.

[mattmathis]

It would be useful for the poll count to be global per daemon, to make it easy to align anomalous server events across TCP connections.

[gfr10598]

It might also be useful to record the interval since the last poll. This will make it easy to determine the exact interval within which the change occurred. Otherwise, we know how many polls occurred in between but we don't know how long the connection was stable, and how recently it changed.