WIP - Proposal for allowing envfile to be defined in docker-compose.yml file

[jonmchan]

This PR does not meet coding standards. Looking for someone to take this up and add tests and documentation. I'm not familiar enough with python or this project to do this.

This is my proposal for resolving #6741. It allows the .env file to be defined from docker-compose.yml file allowing for it to be remapped to .env.docker or /dev/null to not conflict with applications that utilize the .env file.

This implementation evaluates the docker-compose.yml file an extra time, looking for x-env-file. If this is accepted as a solution, a env-file option should be added to the docker-compose schema/spec. I could not find an appropriate section to add a config option like this in the current spec.

This solution preserves the ability to utilize --env-file command line option to override the x-env-file directive in the docker-compose.yml file.

Appreciate any feedback. Thank you.

Resolves #6741

[glours]

Thanks for taking the time to create this issue/pull request!

Unfortunately, Docker Compose V1 has reached end-of-life and we are not accepting any more changes (except for security issues). Please try and reproduce your issue with Compose V2 or rewrite your pull request to be based on the v2 branch and create a new issue or PR with the relevant Compose V2 information.