FEATURE: Allow watched words to be created as a group (#26632)

At the moment, there is no way to create a group of related watched words together.  If a user needed a set of words to be created together, they'll have to create them individually one at a time.

This change attempts to allow related watched words to be created as a group. The idea here is to have a list of words be tied together via a common `WatchedWordGroup` record.  Given a list of words, a `WatchedWordGroup` record is created and assigned to each `WatchedWord` record. The existing WatchedWord creation behaviour remains largely unchanged.

Co-authored-by: Selase Krakani <skrakani@gmail.com>
Co-authored-by: Martin Brennan <martin@discourse.org>

db/migrate/20230515103515_create_watched_word_groups.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+class CreateWatchedWordGroups < ActiveRecord::Migration[7.0]
+  def change
+    create_table :watched_word_groups do |t|
+      t.integer :action, null: false
+
+      t.timestamps
+    end
+  end
+end

db/migrate/20230515131111_add_watched_word_group_id_to_watched_words.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+class AddWatchedWordGroupIdToWatchedWords < ActiveRecord::Migration[7.0]
+  def change
+    add_column :watched_words, :watched_word_group_id, :bigint
+    add_index :watched_words, :watched_word_group_id
+  end
+end