add small coupler AMIP test

[juliasloan25]

To prevent upstream packages from breaking the coupler, we want to add downstream tests in those packages that exercises our AMIP experiment code. It isn't very helpful to run ClimaCoupler's run_tests.jl because while this does test coupler functionality like flux calculation or coupler interfaces with simple simulation objects, it is independent of many important upstream packages and doesn't test their integration.

Ideally, we would be able to add a test running AMIP in our test environment and include this in our run_tests.jl, which upstream packages can easily use. However, the distinction between test and experiments/ClimaEarth environments makes this difficult; many packages used in experiments/ClimaEarth, and specifically those we're interested in testing, are not in the test environment. Because of this, it's easier to add the AMIP experiment test in the experiments/ClimaEarth environment.

We should make a new test that runs the actual AMIP driver in a simple (coarse) setup for just a few timesteps. This can be used by upstream packages to test if their changes will break the interfaces used by the coupler, though it still won't test changes to simulation stability.