DEV: Remove enable_whispers site setting (#19196)

* DEV: Remove enable_whispers site setting

Whispers are enabled as long as there is at least one group allowed to
whisper, see whispers_allowed_groups site setting.

* DEV: Always enable whispers for admins if at least one group is allowed.

db/migrate/20221125173217_remove_enable_whispers_site_setting.rb

@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+class RemoveEnableWhispersSiteSetting < ActiveRecord::Migration[7.0]
+  def up
+    # If enable_whispers was true, insert whispers_allowed_groups or add
+    # staff group to whispers_allowed_groups. This is necessary to keep
+    # the current behavior which has a bypass for staff members.
+    execute <<~SQL
+      INSERT INTO site_settings(name, data_type, value, created_at, updated_at)
+      SELECT 'whispers_allowed_groups', '20', '3', created_at, NOW()
+      FROM site_settings
+      WHERE name = 'enable_whispers' AND value = 't'
+      ON CONFLICT DO NOTHING
+    SQL
+
+    execute <<~SQL
+      UPDATE site_settings
+      SET value = array_to_string(array_append(string_to_array(value, '|'), '3'), '|')
+      WHERE name = 'whispers_allowed_groups' AND
+            EXISTS(SELECT 1 FROM site_settings WHERE name = 'enable_whispers' AND value = 't') AND
+            NOT '3' = ANY(string_to_array(value, '|'))
+    SQL
+
+    # If enable_whispers was false, reset whispers_allowed_groups
+    execute <<~SQL
+      UPDATE site_settings
+      SET value = ''
+      WHERE name = 'whispers_allowed_groups' AND
+            NOT EXISTS(SELECT 1 FROM site_settings WHERE name = 'enable_whispers' AND value = 't')
+    SQL
+
+    # Delete enable_whispers site setting
+    execute <<~SQL
+      DELETE FROM site_settings WHERE name = 'enable_whispers'
+    SQL
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end