Add unique fields only capability to schema.

It would be really great if we could add like a uniqueFieldsOnly parameter to the schema rest functionality.

Recently I've been working in a more professional/complex deployment pipeline where I have a Production, Development, and local parse servers. This brought me to the schema endpoint for deploying structure changes down the pipeline. As you know doing a POST to the schema endpoint with anything that is reserved internally such as objectId, updatedAt, createdAt will return you an error making it impossible to simply take the data returned from a schema request on one parse instance and posting it to another. I was about to write a script to save me from removing these fields by hand and figured it may be worth discussing adding this feature to the server itself as I'm sure others deal with similar scenarios.

Start by tracing the schema REST endpoint and how reserved fields such as objectId, updatedAt, and createdAt are handled. Review the existing issue discussion before deciding the parameter's behavior; done should allow schema data to move between Parse Server instances without manually removing reserved fields.