Disable calls.share_on_join by default (#12401)

This PR changes the default value of the `calls.share_on_join` setting
from `true` to `false`.

Nathan mentioned that project sharing should be opt-in so that projects
aren't shared unless you intend for them to be.

Release Notes:

- Changed the default `calls.share_on_join` value to `false`.

assets/settings/default.json

@@ -170,7 +170,7 @@
     // 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
+    "share_on_join": false
   },
   // Toolbar related settings
   "toolbar": {