Shift option for RRFS-CMAQ

[zmoon]

For a while now, the Online-CMAQ hourly chemical outputs (o3_ave, etc. in the dyn files) have been averages of the previous hour (right-labeled), with forecast-hour 0 being essentially garbage. In this pre-processing script, I shift these variables for better comparison to hourly AirNow, for example, which, like most observational products, is left-labeled in time.

But we can do this in the reader here in MONETIO too. And also deal with potential time duplicates associated with cycles.

cc: @drnimbusrain @bbakernoaa @btang1