Federated migrations fail if custom configurations are present

[Jeff Herald]

Description
An error is thrown when running federated migrations according to the docs if any additional configuration has been added to the config:
{"level":"fatal","ts":1623325336.0228286,"caller":"gateway/config.go:53","msg":"parsing configuration failed","file":"../../clutch-config.yaml","error":"proto: (line 1:624): unable to resolve \"types.google.com/foo.bar.v1.Config\": \"not found\""}

To work around this, i copied the migrations folder into my gateway and added a dummy.go with all of my config packages imported with the blank identifier.

I think a better solution would be to refactor the migration code into a package that can be imported to custom gateways and adopt something like cobra and implement migrations as a sub command.

Expected Behavior
Federated migrations work when additional configurations are present

Actual Behavior
See above.

Version
d744413

Other Context