Add temporal and spatial info to compute_NASC outputs

[leewujung]

Leftover from #1005:

We should consider adding the mean time, latitude, and longitude over the NASC cells with a distance dimension to the compute_NASC output.

See discussions in #1005 (comment)

short of adding the mean time, lon and lat variables (with distance dim) that I mentioned, if we wanted to do it now.

I have mixed feeling about this, mainly two things:

• right now the distance and depth dimensions uses the starting bin edges and not the mean or mid point of the bins (see next point) as the values -- we should probably stick with one scheme
• for the means: should it be true means (as in the mean of the values), or should it just be the middle point of the bins?

Related to #1002

[leewujung]

This can be closed once #1127 is merged.

[emiliom]

Did you mean PR #1167? #1127 is an issue.

Also, add a processing level decorator to compute_NASC in PR #1167, once compute_NASC is ready? @add_processing_level("L4*")

[leewujung]

We can close this now!