add ATR turbulence data

[observingClouds]

Let us start discussing how to add the ATR turbulence data 🥳

In particular:

• describe the difference between turbulence fluctuation data and turbulence moment data
• describe the short-legs, long-legs, longest-legs nomenclature
• discuss how the data sets should be best arranged in the catalog

[observingClouds]

@pebrilou could you maybe comment on some of the above mentioned points and see if we have used the correct metadata. Feel free to expand the description too.