GraphQL API proof of concept: merge request widget endpoint
In #22753 (closed) we established a GraphQL API plan. For %10.0 we're going to produce a proof-of-concept implementation of a GraphQL API, with just enough features to support the merge request widget frontend component. We'll then convert the MR widget to use this API.
The MR widget differs between CE and EE, and includes both read and update operations, so this is a good test of what a GraphQL API implementation will look like in GitLab.