Setting the elixir node cookie value with `RELEASE_COOKIE` instead of with a mix release profile option.

I’m a bit confused about the suggested way to set the elixir cookie value. The fly.io documentation suggests setting the cookie value with a mix release option. But that seems a bit strange to me, because when you want multiple environments, now you have to juggle multiple release profiles too (which has an impact on your Dockerfile, because now you have to pass in a RELEASE_NAME to mix release, and your release scripts are named after that RELEASE_NAME variable).

I found it much easier to just set the RELEASE_COOKIE variable (either as a secret, or as a regular environment variable in fly.toml), which is available anyway at runtime. As documented in the mix release docs about the :cookie option, it takes precedence over the value in releases/COOKIE (which will have a random value, but that’s ok, if you set the RELEASE_COOKIE env variable).

Am I overlooking something here?