Ajax initializer needs a custom rule under module unification

Under module unification, you can't register any old name on the container.

So we will need to either refactor `fastboot/initialzers/ajax.js` or add a custom rule that allows `register('ajax:node')`.

Apps that are experimenting with this stuff can set `moduleConfig.types.ajax = { definitiveCollection: 'main' }` in their own resolver setup to workaround.