Support string projection in plotting functions #1885

Proposed new feature or change:

Holoviz explicitly supports string-valued inputs for projection during plotting operations (see relevant docs page here: https://hvplot.holoviz.org/en/docs/latest/ref/plotting_options/geographic.html).

In uxarray workflows I often find myself starting to explore some data, wanting to plot it, thinking it would be nice to see it with a projection, and then realizing I should have added import cartopy.crs at the top cell of my notebook. Then I have to either add that import inline (which isn't great style), or scroll to the top to add it and then scroll back to where I was working. This is a bit disruptive; the user experience could be improved by instead simply accepting string-valued inputs for projection the same way that holoviz does.

This is a small quality-of-life improvement, so if it requires lots of code to exactly and reliably match holoviz behavior it might not be worthwhile (could close this issue as not planned), but if it isn't too difficult to implement and maintain (e.g., just call a helper function from holoviz directly) it would be nice to have.