Support the DEVONThink x-devonthink-item:// URI scheme

[zakx]

We are using DEVONThink as a document management system. That program generates links to files in its database that look like this:

x-devonthink-item://AF54031A-0F3F-4E44-A5DB-B490E30648B6

Expected behavior: Zulip should automatically recognize this as a valid link.

Current behavior: The link is rendered as text:

Thanks!

[zulipbot]

Hello @zulip/server-markdown members, this issue was labeled with the "area: markdown" label, so you may want to check it out!