Rename the Participant Enrollments Across Sites label on the Data tab

[zackcl]

The "Participant Enrollments Across Sites" label on the Data tab should be renamed to something clearer that better reflects what the number means.

Question: What is the difference between this number on the details page and the number under the "Enrollment" column on the Experiments list table? It seems that the numbers are different for some experiments.

Idea: Would it make sense to rename it to "Total Enrollment for this Experiment" to make it consistent with the Feature Flag's "Exposure" section?

This should be applied to the redesigned UI (it might not be needed for the old experiment design).