With comments, publishing articles, and reactions we had symmetry on two
goals:
- Create a _subject_ (e.g. Comment, Published Article, Reaction)
- Create four _subjects_ within a week.
For page views we only had "Create four _subjects_ within a week." This
PR addes the "Create a _subject_".
To do this required adjusting some tests as they were too specific in
nature (looking at an expected count).
In addition, in consultation with Jennie, I've updated the experiment
order to better reflect some hierarchical importance.
**Rollback considerations:**
This also includes a feature flag that we can explicitly disable if we
overload the application with workers handling reaction goals. Using
`FeatureFlag.accessible?(:field_test_event_single_create_pageview)`
returns `true` unless we explicitly disable this flag.
Related to forem/forem#17673
Related to forem/forem#17669Closesforem/forem#17691
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