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/config/locales/server.en.yml

@@ -2,3 +2,4 @@ en:
   site_settings:
     styleguide_enabled: 'Enable a "/styleguide" path to aid in styling of Discourse'
     styleguide_admin_only: "Limits visibility of the styleguide to admins"
+    styleguide_allowed_groups: "Limits visibility of the styleguide to members of the provided groups"

plugins/styleguide/config/settings.yml

@@ -3,3 +3,11 @@ plugins:
     default: false
   styleguide_admin_only:
     default: true
+    hidden: true
+  styleguide_allowed_groups:
+    default: "1" # auto group admins
+    type: group_list
+    client: false
+    allow_any: false
+    refresh: true
+    validator: "AtLeastOneGroupValidator"