[idea] load directly from ejson

This would require some unfortunate linking or rewriting but it would be kind of excellent to have a single (env/load-from-ejson "config/secrets.ejson" ".env") or something. This would load that ejson file, decrypt it, identify the subtree of environment map, and load it as name/value pairs.

Challenges:

• Would require an additional change detection feature
• A bit more expensive than current evaluation
• New failure modes (key not present, key invalid, ciphertext invalid, JSON invalid, file missing)
• ejson is written in go so we couldn't trivially import it as a lib, and I don't love the idea of shelling out.
• Reimplementing just the decryption side of ejson would be annoying and feels wrong, but maybe not so bad: would be pretty easy and we already have dalek-ed25519 which would be most of the right libraries.

Benefits:

• Disincentivizes writing decrypted secrets to disk
• Appealingly nice integration between our tools.

Start by reviewing the proposed env/load-from-ejson entry point and the current environment-loading flow. Determine how config/secrets.ejson would be decrypted and mapped into .env-style name/value pairs, including the listed failure modes and change detection; done means the integration works without writing decrypted secrets to disk.