Chore: Provide fixed attachment URLs for Channels (#4507)

Prior to this change, The attachment URL sent from Chatwoot to 3rd party integrations like Whatsapp and Facebook
involved a 301 redirect before the original content is served. This causes intermittent breakages for the sent attachments.

fixes: #3632
ref: https://blog.saeloun.com/2021/09/14/rails-7-adds-expiring-urls-to-active-storage.html

spec/models/attachment_spec.rb

@@ -0,0 +1,12 @@
+require 'rails_helper'
+
+RSpec.describe Attachment, type: :model do
+  describe 'download_url' do
+    it 'returns valid download url' do
+      message = create(:message)
+      attachment = message.attachments.new(account_id: message.account_id, file_type: :image)
+      attachment.file.attach(io: File.open(Rails.root.join('spec/assets/avatar.png')), filename: 'avatar.png', content_type: 'image/png')
+      expect(attachment.download_url).not_to eq nil
+    end
+  end
+end

spec/services/facebook/send_on_facebook_service_spec.rb

@@ -57,6 +57,7 @@ describe Facebook::SendOnFacebookService do
         attachment = message.attachments.new(account_id: message.account_id, file_type: :image)
         attachment.file.attach(io: File.open(Rails.root.join('spec/assets/avatar.png')), filename: 'avatar.png', content_type: 'image/png')
         message.save!
+        allow(attachment).to receive(:download_url).and_return('url1')
         ::Facebook::SendOnFacebookService.new(message: message).perform
         expect(bot).to have_received(:deliver).with({
                                                       recipient: { id: contact_inbox.source_id },
@@ -70,7 +71,7 @@ describe Facebook::SendOnFacebookService do
                                                         attachment: {
                                                           type: 'image',
                                                           payload: {
-                                                            url: attachment.file_url
+                                                            url: 'url1'
                                                           }
                                                         }
                                                       },

spec/services/sms/send_on_sms_service_spec.rb

@@ -36,12 +36,14 @@ describe Sms::SendOnSmsService do
         allow(HTTParty).to receive(:post).and_return(sms_request)
         allow(sms_request).to receive(:success?).and_return(true)
         allow(sms_request).to receive(:parsed_response).and_return({ 'id' => '123456789' })
+        allow(attachment).to receive(:download_url).and_return('url1')
+        allow(attachment2).to receive(:download_url).and_return('url2')
         expect(HTTParty).to receive(:post).with(
           'https://messaging.bandwidth.com/api/v2/users/1/messages',
           basic_auth: { username: '1', password: '1' },
           headers: { 'Content-Type' => 'application/json' },
           body: { 'to' => '+123456789', 'from' => sms_channel.phone_number, 'text' => 'test', 'applicationId' => '1',
-                  'media' => [attachment.download_url, attachment2.download_url] }.to_json
+                  'media' => %w[url1 url2] }.to_json
         )
         described_class.new(message: message).perform
         expect(message.reload.source_id).to eq('123456789')