Feat: Support for Microsoft Oauth in Email Channel (#6227)

- Adds the backend APIs required for Microsoft Email Channels

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

db/migrate/20221230113108_add_ms_oauth_token_to_channel.rb

@@ -0,0 +1,8 @@
+class AddMsOauthTokenToChannel < ActiveRecord::Migration[6.1]
+  def change
+    change_table :channel_email, bulk: true do |t|
+      t.jsonb :provider_config, default: {}
+      t.string :provider
+    end
+  end
+end