bring back the notification filter preference (#4225)

It was probably forgotten when we restored the old notifications
behavior.
closes #4222

app/src/main/java/com/keylesspalace/tusky/components/preference/PreferencesFragment.kt

@@ -212,6 +212,13 @@ class PreferencesFragment : PreferenceFragmentCompat(), Injectable {
                     isSingleLineTitle = false
                 }
 
+                switchPreference {
+                    setDefaultValue(true)
+                    key = PrefKeys.SHOW_NOTIFICATIONS_FILTER
+                    setTitle(R.string.pref_title_show_notifications_filter)
+                    isSingleLineTitle = false
+                }
+
                 switchPreference {
                     setDefaultValue(true)
                     key = PrefKeys.CONFIRM_REBLOGS