Command line tool should accept multiple configurations

[1ec5]

The command line tool should accept multiple configuration files or a configuration file plus a URL, merging the various options into a single request. It currently accepts only one configuration file or a URL, which makes it awkward to describe what the argument should be.

/ref https://github.com/mapbox/mapbox-directions-swift/pull/728#discussion_r950625807 /cc @mapbox/navigation-ios