Integration tests with pangeo-forge-runner

[cisaacstern]

Supersedes #563 (for the testing aspect of that PR). This is step 1 of 3 outlined in #569 (comment).

[cisaacstern]

Next steps:

• This:
  

  pangeo-forge-recipes/tests/test_integration.py

  Lines 18 to 19 in f996e5f

  	# TODO: test that json and python configs in docs_src are identical
  	# this way we can confidently use just one of the two

• Maybe rename docs_src/ -> examples/?

Follow-on work:

• After WriteCombinedReference should emit a zarr.storage.FSStore (like StoreToZarr) #608 is complete, un-xfail the kerchunk test. (Could be a follow-on PR.)
• Debug failing narr_opendap and terraclimate recipes. The latter of these two might just be a timeout issue.
• Integration test against Deploy Recipe Action as well.
• Have pangeo-forge-runner integration tests point at the examples directory here.
• Developer docs for how these tests work
• Provide and all install option that includes pangeo-forge-runner

Edit: Outstanding items above ☝️ moved to #609.

[cisaacstern]

Merging this as an improvement to the current status-quo with ample room for further improvement outlined in #609 🙂