fix: Select appropriate email template response (#13051)

* Update email_group.py

Fix: Select appropriate email template response, Welcome email template can be either html or rich text

* refactor: Simpify code

Co-authored-by: Suraj Shetty <13928957+surajshetty3416@users.noreply.github.com>

frappe/email/doctype/email_group/email_group.py

@@ -105,6 +105,6 @@ def send_welcome_email(welcome_email, email, email_group):
 		email=email,
 		email_group=email_group
 	)
-
-	message = frappe.render_template(welcome_email.response, args)
+	email_message = welcome_email.response or welcome_email.response_html
+	message = frappe.render_template(email_message, args)
 	frappe.sendmail(email, subject=welcome_email.subject, message=message)