Support URLs as config files

[Mjaethers]

Related to docker/compose#10360 but I think it makes more sense here.

To make using remote docker compose config files more convenient it should be possible for the user to specify a URL instead of needing to CURL and pipe it in manually.

There are many issues and discussions surrounding adding the ability for users to specify a URL as a config file, however the approach of using the -f flag transparently as opposed to a different --url flag seems cleaner.