DEV: Move core plugin TL -> group settings (#25355)

* DEV: Change poll_minimum_trust_level_to_create to group based setting

New setting is poll_create_allowed_groups

c.f. https://meta.discourse.org/t/changes-coming-to-settings-for-giving-access-to-features-from-trust-levels-to-groups/283408

* DEV: Move styleguide_admin_only to group based setting

Not exactly a TL -> group change, but still part of the
overall effort here:

https://meta.discourse.org/t/changes-coming-to-settings-for-giving-access-to-features-from-trust-levels-to-groups/283408

New setting is styleguide_allowed_groups

plugins/styleguide/spec/integration/access_spec.rb

@@ -1,10 +1,10 @@
 # frozen_string_literal: true
 
-RSpec.describe "SiteSetting.styleguide_admin_only" do
+RSpec.describe "SiteSetting.styleguide_allowed_groups" do
   before { SiteSetting.styleguide_enabled = true }
 
   context "when styleguide is admin only" do
-    before { SiteSetting.styleguide_admin_only = true }
+    before { SiteSetting.styleguide_allowed_groups = Group::AUTO_GROUPS[:admins] }
 
     context "when user is admin" do
       before { sign_in(Fabricate(:admin)) }