Load .env from Compose file's directory and cwd

[Genzer]

This commit loads dotenv .env (exactly that name) from the following location (the later takes precedence):

• The .env file in the Compose file's directory.
• The .env file in the current working directory (invoking podman-compose).

This preserves the behavior prior to 1.1.0 and to match with Docker Compose CLI.

Fix: https://github.com/containers/podman-compose/issues/937

Contributor Checklist:

If this PR adds a new feature that improves compatibility with docker-compose, please add a link to the exact part of compose spec that the PR touches.

All changes require additional unit tests.

[Genzer]

Hi @p12tic, thanks for reviewing!

I just committed the .env files used for manual testing. I was not aware they were ignored by the root .gitignore.

Regards, Genzer

[p12tic]

Rebased.