Refactor pageviewed checkpoint collection

[chicharr]

Current approach is something like this:

• for every page view, we increase a "pages seen" counter in session storage.
• On sampled page views, we send the counter over to RUM

New approach:

• On all page views, we take the "pages seen plus noise" counter, add 1 and add a random integer between -10 and 10 to the counter. This means, for a given visitor, the "pages seen" counter will be 95% noise and 5% signal. This ensures privacy.
• sampled page views, we send the "pages seen plus noise" counter and send it over to RUM