Add metric to track the display of the install browser extension popover

Created by: rrhyne

The browser extension promotes users returning to the product frequently, thus it improves retention. As retention is a primary goal, we should attempt to increase the number of users who install the extension.

The first step in this goal is to fully understand the metrics behind the feature, including its acquisition funnel:

• Add metric to track the display of the "Install browser extension popover"