Add missing attributes to GraphQL project type

We will need the following data that is not currently available in app/graphql/types/project_type.rb.

• issuesAccessLevel - REST API counterpart: lib/api/entities/project.rb#L71
• forkingAccessLevel - REST API counterpart: lib/api/entities/project.rb#L74
• mergeRequestsAccessLevel - REST API counterpart: lib/api/entities/project.rb#L73
• openMergeRequestsCount
• accessLevel - Should return Types::AccessLevelType