DEV: Store theme sprites in the DB (#20501)

Let's avoid fetching sprites from the CDN during page rendering.

db/migrate/20230224193734_create_theme_svg_sprite.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+class CreateThemeSvgSprite < ActiveRecord::Migration[7.0]
+  def change
+    create_table :theme_svg_sprites do |t|
+      t.integer :theme_id, null: false
+      t.integer :upload_id, null: false
+      t.binary :sprite, null: false
+
+      t.timestamps
+    end
+
+    add_index :theme_svg_sprites, :theme_id, unique: true
+  end
+end