chore: Provider API prototype (#3112)

Enabling Support for Whatsapp via 360Dialog as a prototype for the provider APIs. 

Co-authored-by: Pranav Raj S <pranav@chatwoot.com>

spec/factories/channel/channel_whatsapp.rb

@@ -0,0 +1,11 @@
+FactoryBot.define do
+  factory :channel_whatsapp, class: 'Channel::Whatsapp' do
+    sequence(:phone_number) { |n| "+123456789#{n}1" }
+    account
+    provider_config { { 'api_key' => 'test_key' } }
+
+    after(:create) do |channel_whatsapp|
+      create(:inbox, channel: channel_whatsapp, account: channel_whatsapp.account)
+    end
+  end
+end