Enable "displaying application used to post" setting by default (#9994)

related: https://github.com/tootsuite/mastodon/pull/9897#issuecomment-461093615

config/settings.yml

@@ -26,7 +26,7 @@ defaults: &defaults
   expand_spoilers: false
   preview_sensitive_media: false
   reduce_motion: false
-  show_application: false
+  show_application: true
   system_font_ui: false
   noindex: false
   theme: 'default'