Add Project.forkedFrom to graphql api

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What does this MR do and why?

Add Project.forkedFrom to graphql api, because this data is currently only available from the REST API.

References

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MR acceptance checklist

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Screenshots or screen recordings

No UI Changes.

How to set up and validate locally

1. Fork a project
2. Execute the query for the forked project

   query forkedFrom {
     project(fullPath: "<path>") {
       fullPath
       forkedFrom {
         fullPath
       }
     }
   }