feat: Add createUpload GraphQL mutation

[sentry]

This PR implements the createUpload GraphQL mutation, which was previously missing from the API schema. The absence of this mutation caused GraphQLError: Cannot query field 'createUpload' on type 'Mutation' when clients attempted to use it.

The implementation includes:

• Defining CreateUploadInput and CreateUploadPayload types in new .graphql schema files.
• Creating the resolve_create_upload resolver to handle the mutation logic.
• Registering the new mutation in apps/codecov-api/graphql_api/types/mutation/mutation.graphql and apps/codecov-api/graphql_api/types/mutation/mutation.py.
• Integrating the new mutation module into apps/codecov-api/graphql_api/types/mutation/__init__.py to ensure it's loaded correctly.

This change makes the createUpload functionality accessible via the GraphQL API.

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Look, I get it. The entity doing business as "Sentry" was incorporated in the State of Delaware in 2015 as Functional Software, Inc. In 2022 this entity acquired Codecov and as result Sentry is going to need some rights from me in order to utilize my contributions in this PR. So here's the deal: I retain all rights, title and interest in and to my contributions, and by keeping this boilerplate intact I confirm that Sentry can use, modify, copy, and redistribute my contributions, under Sentry's choice of terms.

Fixes API-E92