DEV: Correct historical badge and user_badge index discrepancies (#10017)

Badge and user_badge tables were created using add_column index: true
When the migration was written, `index: true` was a no-op for non-reference columns
Since then, rails made it work 9a0d35e820
This migration adds the index to very old sites, so that we have a consistent state

db/migrate/20201006172700_create_missing_badge_indexes.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+# Badge and user_badge tables were created using add_column index: true
+# When the migration was written, `index: true` was a no-op for non-reference columns
+# Since then, rails made it work https://github.com/rails/rails/commit/9a0d35e820464f872b0340366dded639f00e19b9
+# This migration adds the index to very old sites, so that we have a consistent state
+
+# frozen_string_literal: true
+
+class CreateMissingBadgeIndexes < ActiveRecord::Migration[6.0]
+  def up
+    execute "CREATE INDEX IF NOT EXISTS index_user_badges_on_user_id ON public.user_badges USING btree (user_id)"
+    execute "CREATE INDEX IF NOT EXISTS index_badges_on_badge_type_id ON public.badges USING btree (badge_type_id)"
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end