Follow NEP29 and set lower bounds for the dependencies (all minor
versions from the last 2 years). The only exception is xrft, which is
new and likely requires v1.0 to work with Harmonica. Setup CI to run on
lowest Python with lowest dependencies, highest Python with highest
dependencies, and highest Python with optional dependencies. Use
Dependente to extract the version information from setup.cfg instead of
the custom export tool we had.

Some of the test we are running depend on the grid method of Verde
gridders to allow the get coordinates as arguments. This feature was
added in Verde 1.7.0.