Chart ETP usage

[openjck]

Arthur Edelstein has requested that we chart ETP usage, perhaps as a second line/population of the tracking protection chart on the Usage Behavior page.

More information here:

https://docs.google.com/document/d/1t4kOqaeb0KxQG0Gk12jIi4BYReXU_blj-DURAGgBxck/edit

[openjck]

@SuYoungHong, I believe the data engineering work is unblocked now that the expiration has been extended in Firefox 70. Is that correct? Would it be possible to make this a second population/line on the existing tracking protection metric, as we do with languages?

[openjck]

Frank is going to get this done by the end of next week. It'll be a separate line on the Tracking Protection chart.