Automatically add .env variables to repo secrets

[noamross]

• See https://gist.github.com/philip-gai/2b21293b178aa6ea6903e99cc1c32c4f for an action that modifies secrets
• After git-crypt unlocking (in the same step), run a loop over the lines in .env adding all variables to secrets
  • cat .env >> $GITHUB_ENV is an option for just adding them to the environment, but that may not obfuscate them in logs and such.
  • use ${{ secret.VARIABLE}} syntax elsewhere.
  • Should this be a job rather than a step? Should other jobs depend on it?