Add link to godot-proposals in the issue template

To reduce confusion over where to propose enhancements to the engine
itself

.github/ISSUE_TEMPLATE/config.yml

@@ -5,6 +5,10 @@ contact_links:
  url: https://godotengine.org/community
  about: Please ask for technical support on one of the other community channels, not here.
 
+ - name: Godot proposals
+ url: https://github.com/godotengine/godot-proposals
+ about: Please submit engine feature proposals on the Godot proposals repository, not here.
+
  - name: Main Godot repository
  url: https://github.com/godotengine/godot
  about: Report engine bugs on the main Godot repository