Support for multiple .env files: .env.<mode>

[BierDav]

Is your feature request related to a problem? Please describe.
We use api keys to download external dependencies, but you mustn't include them in the git repository. So we define it in the .env.local file, which is excluded from git. But we also need to define other variables that should be stored in git. Those we want to store in .env.

Describe the solution you'd like
To support this behaviour it would be great, to be able to specify multiple files in dotenv.filename which will be all read and override each other in the order specified

Describe alternatives you've considered
Currently we use gradle.properties as an alternative to the .env files