Framework: Mutations

[misha-kotov]

As a Magento developer, I want GraphQL to support mutations to create/update/delete entities in the system via GraphQL so that I can build basic ecommerce front-end experiences for my customers entirely in GraphQL.

This epic will contain a set of relevant tasks that will enable GraphQL to perform mutations. The focus is on the framework piece that will be leveraged to build out concrete mutations in various parts of the system. These specific mutations are out of scope here and are captured in other epics (ex: My Account)

Examples of desired mutations:
-- add, modify, or remove the billing address on the Cart
-- add, modify, or remove the shipping address on the Cart
-- add, modify, or remove items in the Cart
-- add or remove coupons on the Cart
-- add or remove gift cards on the Cart