Add support for `fdroidrepo://` URLs

fdroidrepo:// is supported by the official client to add a new HTTP repository (and fdroidrepos:// for HTTPS). This is handy because it allows a website to expose a button with a link which directly opens up the F-Droid store page to add a new repository with all the info pre-filled.

Can you please share a sample of this, It would be helpful

TBH the only implementation I know is the official client, so reference should be that source code. For details how this works if you provide a link like this one

fdroidrepos://https://gitjournal.io/fdroid/repo/
fdroidrepos://https://gitjournal.io/fdroid/repo/?fingerprint=E2EE4AA4380F0D3B3CF81EB17F5E48F827C3AA77122D9AD330CC441650894574

when clicked/opened shows the available apps that implement the protocol and thus can open it. F-Droid official client will be on the list and when selected, directly opens the dialog to add a new repo with the given data after the fdroidrepos:// prefilled

One thing I discovered is with missing fdroid/repo/ the links are not recognized:

fdroidrepos://https://store.nethunter.com/repo/
fdroidrepos://https://store.nethunter.com/repo/?fingerprint=7E418D34C3AD4F3C37D7E6B0FACE13332364459C862134EB099A3BDA2CCF4494

This may be a bug or intentional, could not find any documentation so far

I can't even make them work on Official client

and idk how to implement this perfectly as there is no documentation

AFAIK the fdroidrepos:// just have to be replaced with https:// as Neo Store does it here: https://github.com/NeoApplications/Neo-Store/commit/db08d75e7bb20591971745dc045a8d54423b1cd9

So a valid example should be like this:

• fdroidrepos://releases.threema.ch/fdroid/repo?fingerprint=5734E753899B25775D90FE85362A49866E05AC4F83C05BEF5A92880D2910639E

which's listed here: https://threema.ch/en/faq/libre_installation