Introducing new .env file support in 1Password

Great feature, however I encountered some issues when trying to make use of it:

- There is currently no feature to reference existing 1Password items, which means I have to maintain stuff like tokens, passphrases etc. in two places when using the Environments feature.
- It would be great to support actually setting the environment variables - for example, for usage in Terraform variables. As a workaround, I tried to use `direnv` (on macOS) - but it does not recognize the 'file' created by 1Password, even when mounted/decrypted:

# When in folder with .envrc created/mounted by 1Password:

> direnv allow .
direnv: error .envrc file not found

- Another improvement would be to add another mounting option 'Terraform variable' which creates a `.tfvars` file at the desired location, and prefixes the variables with `TF_VAR` - this would cover a common use case and also remove the need for creating separate variables with that prefix.

But great idea with lots of potential!