feat(coderd): add new dispatch logic for coder inbox (#16764)

This PR is [resolving the dispatch part of Coder
Inbocx](https://github.com/coder/internal/issues/403).

Since the DB layer has been merged - we now want to insert notifications
into Coder Inbox in parallel of the other delivery target.

To do so, we push two messages instead of one using the `Enqueue`
method.

coderd/database/queries/notifications.sql

@@ -84,6 +84,7 @@ SELECT
     nm.method,
     nm.attempt_count::int                                                 AS attempt_count,
     nm.queued_seconds::float                                              AS queued_seconds,
+    nm.targets,
     -- template
     nt.id                                                                 AS template_id,
     nt.title_template,