chore: Provider APIs for SMS Channel - Bandwidth (#3889)

fixes: #3888

spec/factories/channel/channel_sms.rb

@@ -0,0 +1,16 @@
+FactoryBot.define do
+  factory :channel_sms, class: 'Channel::Sms' do
+    sequence(:phone_number) { |n| "+123456789#{n}1" }
+    account
+    provider_config do
+      { 'account_id' => '1',
+        'application_id' => '1',
+        'api_key' => '1',
+        'api_secret' => '1' }
+    end
+
+    after(:create) do |channel_sms|
+      create(:inbox, channel: channel_sms, account: channel_sms.account)
+    end
+  end
+end