Rename TrackUniqueActions to TrackUniqueEvents

What does this MR do?

In this MR we rename the module TrackUniqueActions to TrackUniqueEvents.

The class TrackUniqueActions can be misleading because what it in fact does is to track events. For example, in 92e3de76 some work was done to rename some methods and logic, like track_action to track_event, to make it more clear that the module was dealing with Events. Nevertheless, the name wasn't changed.

In !39694 (merged) we're going to introduce a class that in fact tracks actions (not linked to the Event model), which is a better candidate for TrackUniqueActions.

Does this MR meet the acceptance criteria?

Conformity

• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content