mail/snappymail: Fix autoconfig

When configuring a new domain and hit the Autoconfig button, an
error is occurred due the missing SimpleXML extension.

```
[2024-03-09 07:18:28.749][72d59c31] PHP[WARNING]: file_get_contents(https://autoconfig.disroot.org/.well-known/mail-v1.xml?emailaddress=test%40disroot.org): Failed to open stream: HTTP request failed! HTTP/1.1 403 Forbidden
 /usr/local/www/snappymail/snappymail/v/2.35.2/app/libraries/RainLoop/Providers/Domain/Autoconfig.php [line:64, code:2]
[2024-03-09 07:18:30.360][72d59c31] PHP[WARNING]: file_get_contents(https://disroot.org/.well-known/autoconfig/mail/config-v1.1.xml): Failed to open stream: HTTP request failed! HTTP/1.1 404 Not Found
 /usr/local/www/snappymail/snappymail/v/2.35.2/app/libraries/RainLoop/Providers/Domain/Autoconfig.php [line:64, code:2]
[2024-03-09 07:18:31.518][72d59c31] SERVICE[WARNING]: Call to undefined function simplexml_load_string()
```

After installing the simplexml extension, it just shows a bunch of
warnings, but Autoconfig works and configures the parameters
without user intervention.

```
[2024-03-09 07:20:27.683][64f93497] PHP[WARNING]: file_get_contents(https://autoconfig.disroot.org/.well-known/mail-v1.xml?emailaddress=test%40disroot.org): Failed to open stream: HTTP request failed! HTTP/1.1 403 Forbidden
 /usr/local/www/snappymail/snappymail/v/2.35.2/app/libraries/RainLoop/Providers/Domain/Autoconfig.php [line:64, code:2]
[2024-03-09 07:20:29.426][64f93497] PHP[WARNING]: file_get_contents(https://disroot.org/.well-known/autoconfig/mail/config-v1.1.xml): Failed to open stream: HTTP request failed! HTTP/1.1 404 Not Found
 /usr/local/www/snappymail/snappymail/v/2.35.2/app/libraries/RainLoop/Providers/Domain/Autoconfig.php [line:64, code:2]
```
PR:		277611
MFH:		2024Q1