Explicit naming for schema extensions in the config file
Explicit naming for schema extensions in the config file

Summary:
In the JS compiler we have an `extensions` option: which is indicating file extensions we need to look at.

In rust config, we also have the `extensions` option in the config, but these extensions are client schema extensions.

Let's use explicit naming in the rust config.

Reviewed By: rbalicki2

Differential Revision: D32281904

fbshipit-source-id: 2c22b2774bc56c3d589a457a44861133c7b8afd6

kassens/relay,kassens/relay,facebook/relay,josephsavona/relay,voideanvalue/relay,facebook/relay,wincent/relay,josephsavona/relay,facebook/relay,xuorig/relay,facebook/relay,xuorig/relay,xuorig/relay,voideanvalue/relay,wincent/relay,xuorig/relay,voideanvalue/relay,wincent/relay,wincent/relay,kassens/relay,facebook/relay,josephsavona/relay,facebook/relay,xuorig/relay,kassens/relay,voideanvalue/relay,voideanvalue/relay,kassens/relay,wincent/relay,wincent/relay,voideanvalue/relay,kassens/relay,xuorig/relay