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>

spec/requests/admin/watched_words_controller_spec.rb

@@ -86,6 +86,17 @@ RSpec.describe Admin::WatchedWordsController do
         expect(WatchedWord.find_by(id: watched_word.id)).to eq(nil)
         expect(UserHistory.where(action: UserHistory.actions[:watched_word_destroy]).count).to eq(1)
       end
+
+      it "should delete watched word group if it's the last word" do
+        watched_word_group = Fabricate(:watched_word_group)
+        watched_word.update!(watched_word_group: watched_word_group)
+
+        delete "/admin/customize/watched_words/#{watched_word.id}.json"
+
+        expect(response.status).to eq(200)
+        expect(WatchedWordGroup.exists?(id: watched_word_group.id)).to be_falsey
+        expect(WatchedWord.exists?(id: watched_word.id)).to be_falsey
+      end
     end
   end
 
@@ -104,17 +115,24 @@ RSpec.describe Admin::WatchedWordsController do
       before { sign_in(admin) }
 
       it "creates a word with default case sensitivity" do
-        post "/admin/customize/watched_words.json", params: { action_key: "flag", word: "Deals" }
+        expect {
+          post "/admin/customize/watched_words.json",
+               params: {
+                 action_key: "flag",
+                 words: %w[Deals Offer],
+               }
+        }.to change { WatchedWord.count }.by(2)
 
         expect(response.status).to eq(200)
         expect(WatchedWord.take.word).to eq("Deals")
+        expect(WatchedWord.last.word).to eq("Offer")
       end
 
       it "creates a word with the given case sensitivity" do
         post "/admin/customize/watched_words.json",
              params: {
                action_key: "flag",
-               word: "PNG",
+               words: ["PNG"],
                case_sensitive: true,
              }