Add global validation

[dgergel]

This PR adds global validation for tasmax, tasmin, dtr and pr. It supports validation of cleaned CMIP6, bias corrected and downscaled data for historical and future time periods. It includes a new service called validate with CLI interface:

dodola validate /path/to/dataset_to_validate.zarr \
--v "tasmax" 
--data "bias_corrected"
--time "future"

Validation includes the following checks for cleaned CMIP6, bias corrected and downscaled zarrs, historical and projection period:

For all variables:

• output zarrs include the expected variable names
• NaNs
• output zarrs contain the correct number of timesteps

For tasmax and tasmin:

• temperature range

For DTR:

• DTR range
• negative values

For precip:

• negative values
• maximum values are reasonable

closes #69

[brews]

Innnnteresting! @dgergel, I see what you're going for. I fear that this is going to read in a huge zarr store all into memory as it's written (I don't know if you've checked this) but I also think we have enough to pull out core functions and figure out a way to work around this if it ends up really being a problem.

I appreciate the unit tests!

Two small documentation things I'd recommend before you merge this.

1. Could you update the PR description above and quickly outline what we're actually checking for the different arguments so it's clear what this new behavior is exactly. You explain the command but it would help to have a quick new-person friendly description of what's going on beyond just "validation".

2. Also, could you please update the changelog with this addition?

👍

[dgergel]

@brews this should be all ready - lmk if you see anything else to update before I merge!

[brews]

Thanks, @dgergel. I think we're set to throw some data at this and take it from there. Merge away!