Improve our phishing warning page Metrics

[ElvirCe]

Additionally, we should add some metrics to this page to help us understand the frequency of occurrence and usage of this phishing warning. We'll add a new events: Phishing Page Displayed.

Phishing Page Displayed has the following properties:

url: url that triggered the phishing warning page to be displayed

And for the External Link Clicked, as discussed with Dan Miller and Bárbara Schorchit, it will be done in an another ticket.

This ticket is the second part of the ticket #16602