Handle timestampVal type in stats.py

[jbfuzier]

Hello,

This PR add handling for timestampVal, this is used when stats queries return timebuckets, example :

events:
            $e.metadata.log_type="CS_EDR"
            $log_type = $e.metadata.log_type
match:
            $log_type by 5m
outcome:
            $total = math.round(count($e.metadata.id)/300)

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[mihirvala08]

Hi @jbfuzier, could you please sign CLA here https://cla.developers.google.com/clas ?
Let me know once done, So I can re run the check.

[jbfuzier]

Hello,

Thanks, done.

[mihirvala08]

/run-integration-tests 3b11501