Error check and dump metadata function

[ifranda]

I thought I'd open a small PR to test run making changes to the Python api. I've made two changes:

1. When RGB colors are converted to HSV, make a check to verify the list is of length 3. I think this stops the kernel from crashing when using incorrect inputs with SetColorRGBList
2. Added a DumpVarMetadata function for datasets. Some of the examples printed out the metadata manually, and I thought it would be nice to have it integrated into the package.

I've tested it out and I think it's working as intended, but let me know if there's anything else I should watch out for!

[NihanthCW]

Great! You can assign Stas as a reviewer and discuss any questions tomorrow.

[StasJ]

Looks good, thanks! I would suggest implementing DumpVarMetadata as __str__ and include dimensions and coordinates, similar to Xarray.

[ifranda]

Just made the change! We can definitely talk more about what's being returned here if we have other ideas.

[StasJ]

Looks good, thanks.