News' "add this RSS feed" functionality doesn't honor the HTTPS upgrade setting

[fmarier]

Steps To Reproduce:

1. Enable Brave News
2. In Brave settings (brave://settings/shields), set "Upgrade connections to HTTPS" to "Strict"
3. Open WireShark. Enable capturing. Set the display filter in WireShark to http
4. Visit https://fmarier.github.io/brave-testing/news-add-rss.html
5. Click the feed icon in the URL bar
6. Go back to WireShark. You can see a plaintext request sent to 172.105.6.87

Actual

Expected

The request should be upgraded to HTTPS and no HTTP request should be visible in WireShark.

Originally reported at https://hackerone.com/reports/2502007

[fmarier]

The other thing that this suggests is that we are likely not running these URLs through our privacy filters (e.g. debouncer, query string filter).

[fmarier]

To confirm, I updated the test page to add an fbclid parameter to the URL and it doesn't get stripped out:

[bsclifton]

cc: @LorenzoMinto