Modify upstream provider from command line [APE-1471]

[xrchz]

Overview

Provide a simple overview of what you wish to see added. Please include:

• What you are trying to do
• Why Ape's current functionality is inadequate to address your goal

Provide an override to the config file upstream provider on the command line or in an environment variable. Sometimes projects will include a provider in the config that is different from the one we want to use locally. Changing the config file locally can be easy to mess up with git accidentally committing the change.

Specification

Describe the syntax and semantics of how you would like to see this feature implemented. The more detailed the better!

Remember, your feature is much more likely to be included if it does not involve any breaking changes.

Add --upstream-provider ... command line option

Dependencies

Include links to any open issues that must be resolved before this feature can be implemented.