feat: use custom config path with --config arg

[serrg]

I would like to propse new optional --config argument for passing custom path to the config

To be: make-federated-types --config ./path/to/my/config.json --outputDir ../../my_types/

[serrg]

@crutch12 WDYT about this new argument? It is useful when you store your configs outside of root repo directory.
cc @gthmb

[gthmb]

Hey guys, I lost control over this repo when I changed jobs so I cannot merge. Thanks for contributing - I will ping my contacts at Pix to merge!

[gthmb]

Thanks for your patience! And a big thanks for helping make this package better!