FIX: Don't store translated trust level names in anonymous cache (#13224)

Refactors `TrustLevel` and moves translations from server to client

Additional changes:
  * "staff" and "admin" wasn't translatable in site settings
  * it replaces a concatenated string with a translation
  * uses translation for trust levels in users_by_trust_level report
  * adds a DB migration to rename keys of translation overrides affected by this commit

spec/models/trust_level_setting_spec.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe TrustLevelSetting do
+  describe ".values" do
+    it "returns translated names" do
+      TranslationOverride.upsert!(I18n.locale, "js.trust_levels.names.newuser", "New Member")
+
+      value = TrustLevelSetting.values.first
+      expect(value[:name]).to eq(I18n.t("js.trust_levels.detailed_name", level: 0, name: "New Member"))
+      expect(value[:value]).to eq(0)
+    end
+  end
+end