Add GraphQL CRUD Mutations for File "Viewed" Persistence
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[From this comment](https://gitlab.com/gitlab-org/gitlab/-/issues/322798#note_524582021).
Given the [anticipated implementation for the backend](https://gitlab.com/gitlab-org/gitlab/-/issues/322798#note_524066907), the ~frontend will need to add the "CRUD" behavior for connecting to the backend:
- "Create" a file review
- "Delete" a file review
- "Read" the existing file reviews
This issue assumes we already [have a GraphQL implementation in the frontend](https://gitlab.com/gitlab-org/gitlab/-/issues/324112).
issue