Do more on channel join (#7268)

This change makes it so that if you are the first to join a channel,
your project is automatically shared.

It also makes it so that if you join a channel via a link and there are
no shared projects, you open the notes instead of an empty workspace
with nothing.

This is to try and address the discoverability of project sharing: we've
had
two reviews that have talked about channels, but not talked about
sharing
projects into them, which makes me suspect they didn't know about the
feature.

Release Notes:

- Added a setting `share_on_join` (defaulting to true). When set, and
you join an empty channel, your project is automatically shared.

assets/settings/default.json

@@ -104,8 +104,10 @@
   "show_whitespaces": "selection",
   // Settings related to calls in Zed
   "calls": {
-    // Join calls with the microphone muted by default
-    "mute_on_join": false
+    // Join calls with the microphone live by default
+    "mute_on_join": false,
+    // Share your project when you are the first to join a channel
+    "share_on_join": true
   },
   // Scrollbar related settings
   "scrollbar": {