Windows Installer: Add xmpp URI handling
This enables Gajim to handle xmpp: URIs on Windows. Gajim’s installer will offer a choice for that (similar to other choices, like whether to create a desktop icon or not).
Fixes #10122 (closed)
We still need translations for the following strings to Italian, Spanish, and Hebrew:
- "Open xmpp links with Gajim"
- "Enables Gajim to open xmpp links (e.g. a group chat linked on a website)."