Add timestamp handling for telemetry submission in recordings

[daniestevez]

Currently the timestamp for telemetry submission is taken from the system time, so recordings don't have the correct timestamp. By adding and tracking timestamps appropriately in the data source, we could have good timestamp tagging arriving into the telemetry submit block. However, this doesn't seem trivial.

[daniestevez]

Note that something like this has been implemented by using the --start_time and --throttle parameters. However, the idea is to eventually be able to count recording samples rather that playing back at 1x speed and using the wall time.