Add Endpoint to compute Chart Timestamps

[camdnnn]

Currently the timestamp values of a chart are computed by offsetting all the timestamp by the datetime at the start of the file. To account for discrepancies between the timestamps and gps dmyhms. This should be fixed by adding a new endpoint to the backend which explicitly calculates the timestamps of the file in datetime with a higher number of references to the gps time. The goal of this change is to hopefully better account for errors in the teensy timestamp.