Spanish translation

[emlys]

To support multiple languages, this PR introduces a directory for each language:

• Move the English source docs into source/en
• Add all the Spanish source docs into source/es

They all share the same conf.py file.

Changes to the build process:

• make html now builds each language as an independent sphinx project.
• make redirect builds another copy of the docs where each page redirects to the new location of that page in English (ie. build/html/foo.html -> build/html/en/foo.html). That way we won't break links that point to the old user's guide location.
• The github actions workflow now uploads dev builds of the user's guide to the dev builds bucket.
  • Like with invest, this doesn't work on PRs - only on your fork. You'll need to add the GCP authentication secret as well.
  • Because we don't version the user's guide, only the "latest" dev version is hosted for each user. This is the version most recently built on your fork.
  • For example: https://storage.googleapis.com/natcap-dev-build-artifacts/invest-userguide/emlys/latest/es/index.html

[emlys]

Thanks @phargogh! I also had to remove the reference to ws_id in SDR.