feat: Builder for creating Campaign conversations (#2192)

- Builder for creating Campaign conversations
- Widget endpoint to fetch the campaigns

spec/controllers/api/v1/widget/campaigns_controller_spec.rb

@@ -0,0 +1,31 @@
+require 'rails_helper'
+
+RSpec.describe '/api/v1/widget/campaigns', type: :request do
+  let(:account) { create(:account) }
+  let(:web_widget) { create(:channel_widget, account: account) }
+  let!(:campaign_1) { create(:campaign, inbox: web_widget.inbox, enabled: true, account: account) }
+  let!(:campaign_2) { create(:campaign, inbox: web_widget.inbox, enabled: false, account: account) }
+
+  describe 'GET /api/v1/widget/campaigns' do
+    let(:params) { { website_token: web_widget.website_token } }
+
+    context 'with correct website token' do
+      it 'returns the list of enabled campaigns' do
+        get '/api/v1/widget/campaigns', params: params
+
+        expect(response).to have_http_status(:success)
+        json_response = JSON.parse(response.body)
+        expect(json_response.length).to eq 1
+        expect(json_response.pluck('id')).to include(campaign_1.display_id)
+        expect(json_response.pluck('id')).not_to include(campaign_2.display_id)
+      end
+    end
+
+    context 'with invalid website token' do
+      it 'returns the list of agents' do
+        get '/api/v1/widget/campaigns', params: { website_token: '' }
+        expect(response).to have_http_status(:not_found)
+      end
+    end
+  end
+end