Storing a lot of environment variables

It seems to be wp-cli.yml cannot hold envs.
We use a WP installation depending on many envs.
Now I keep `putenv()`-s in

```yaml
require:
  - /home/user/website/wp-cli-envs.php
```

Could we implement this?

```yaml
env:
  DB_NAME: "instahuu"
```

