GraphQL: Clean up alpha elements in Runner queries and make them official

We've been creating fields and mutations behind alpha deprecation, in order to maintain flexibility to change the API surface if needed. After more than a year of doing that, there are now many APIs which we are confident they won't change in the foreseeable future. We should take the time to revisit them and officialize them by removing the alpha flag.

API	Introduced	Rationale for removal
RunnerType.upgradeStatus	%14.10	The API hasn't changed since introduction, so the risk of releasing it is non-existent.
RunnerManagerType.upgradeStatus	%16.1	The API hasn't changed since introduction, so the risk of releasing it is non-existent.
CiJobsStatistics.queuedDuration	%15.8	Although queuedDuration is marked as alpha, the parent type is not, so right now it is basically an empty type. It seems like this API won't be changing anytime soon, so we could release it.