Improve incorrectly flagged reporting flow

[holantonela]

Now that our phishing warning page receives reports from multiple sources, we should ensure that users or site owners reporting a false positive can do it helpful.

One idea is to have pre-filled issues. I'm making an example here.

https://github.com/MetaMask/phishing-warning/issues/new?body=domain:[$bad_flagged_url], source: [$name_of_the_list]

We should provide all this information without affecting users' privacy while allowing them to open tickets in an open repo for human review.

This issue must be opened when the user clicks/tap the link [please report a detection problem].