Open zulipchat.com and chat.zulip.org links in mobile app

[WesleyAC]

It would be nice if the Zulip app was show as an option to open links to zulip instances. While neither Android nor iOS allow apps to register to handle a dynamic set of links, we can specifically handle *.zulipchat.com and chat.zulip.org links in the app, which would probably be good. This work would also likely be useful towards handling zulip://-style links.

See #mobile > deep links for some chat about this.

[WesleyAC]

I noticed today that we already have a appOwnDomains, which presumably we should keep up-to-date with this.

I think it would be hard to share code here, but it does make me more comfortable about special-casing hosted zulip instances, and we should add a comment in all of the places that we have this set of domains to keep them updated in sync.

[chrisbobbe]

We got another request for this feature today: https://chat.zulip.org/#narrow/stream/48-mobile/topic/Bug.20reports/near/1480790

[gnprice]

Related issues:

• Implement deep Link Functionality. (Android) #4751
• Enable deep link for iOS #4776

and PR:

• Implement deep link functionality and enable it for android. #4775

Those are all for zulip:// URLs.