DEV: pluck_first

Doing .pluck(:column).first is a very common pattern in Discourse and in
most cases, a limit cause isn't being added. Instead of adding a limit
clause to all these callsites, this commit adds two new methods to
ActiveRecord::Relation:

pluck_first, equivalent to limit(1).pluck(*columns).first

and pluck_first! which, like other finder methods, raises an exception
when no record is found

lib/freedom_patches/pluck_first.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+class ActiveRecord::Relation
+  def pluck_first(*attributes)
+    limit(1).pluck(*attributes).first
+  end
+
+  def pluck_first!(*attributes)
+    items = limit(1).pluck(*attributes)
+
+    raise_record_not_found_exception! if items.empty?
+
+    items.first
+  end
+end
+
+module ActiveRecord::Querying
+  delegate(:pluck_first, :pluck_first!, to: :all)
+end