Parameter `distinct_by_branch` config in custom experiment config should override outcome definition

[mikewilli]

It appears that the parameter config distinct_by_branch in a custom experiment config is not properly overriding the value in the outcome. See here for example: https://app.circleci.com/pipelines/github/mozilla/metric-hub/3985/workflows/2649a9d5-97cb-40b5-af12-bd98cf44c0aa/jobs/8861