Background
In T404058: Add MetricsPlatform to gated extensions, I decided not to make MetricsPlatform a gated extension but rather to adopt the approach suggested in https://phabricator.wikimedia.org/T403560#11158409 and make MetricsPlatform and GrowthExperiments depend on one another. This task covers doing that.
AC
- MetricsPlatform's tests run when GrowthExperiments' tests run
- GrowthExperiments' test run when MetricsPlatform's tests run