FEATURE: theme_modifiers can depend on theme settings (plus serialize_post_user_badges) (#29227)

Theme modifiers can now be defined as theme settings, this allows for
site operators to override behavior of theme modifiers.

New syntax is:

```
{
    ...
   "modifiers": {
      "modifier_name": {
         "type": "setting",
         "value": "setting_name"
      }
   }
}
```

This also introduces a new theme modifier for serialize_post_user_badges. Name of badge must match the name of the badge in the badges table. The client-side is updated to load this new data from the post-stream serializer.

Co-authored-by: David Taylor <david@taylorhq.com>

db/migrate/20241011033602_add_post_badges_to_theme_modifiers.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+class AddPostBadgesToThemeModifiers < ActiveRecord::Migration[7.1]
+  def change
+    add_column :theme_modifier_sets, :serialize_post_user_badges, :string, array: true
+    add_column :theme_modifier_sets, :theme_setting_modifiers, :jsonb
+  end
+end