Improve SMTP authentication and Fix user creation bugs (#16612)

* Improve SMTP authentication, Fix user creation bugs and add LDAP cert/key options

This PR has two parts:

Improvements for SMTP authentication:

* Default to use SMTPS if port is 465, and allow setting of force SMTPS.
* Always use STARTTLS if available
* Provide CRAM-MD5 mechanism
* Add options for HELO hostname disabling
* Add options for providing certificates and keys
* Handle application specific password response as a failed user login
instead of as a 500.

Close #16104

Fix creation of new users:

* A bug was introduced when allowing users to change usernames which
prevents the creation of external users.
* The LoginSource refactor also broke this page.

Close #16104

Signed-off-by: Andrew Thornton <art27@cantab.net>

web_src/js/index.js

@@ -1992,7 +1992,9 @@ function initAdmin() {
           $('#password').attr('required', 'required');
         }
       } else {
-        $('#user_name').attr('disabled', 'disabled');
+        if ($('.admin.edit.user').length > 0) {
+          $('#user_name').attr('disabled', 'disabled');
+        }
         $('#login_name').attr('required', 'required');
         $('.non-local').show();
         $('.local').hide();