When the database used by GrowthExperiments is in readonly mode, any write attempts result in an exception being thrown. For user-facing features this is not ideal; also it might interrupt something that would otherwise work (e.g. user registration). We should ensure everything is behind a wfReadOnly() check or prepared to handle DBReadOnlyError.
This is time-sensitive because of T281212: Restart x1 database master (db1103).