Add error message for missing openssl extension

[grandeljay]

When the OpenSSL (openssl) PHP extension is deactivated, the MMLC does not load causing a fatal error without any information on what the issue is. The error message is completely empty making the log entry useless.

Excerpt from /logs/error/*.log:

[2025-08-27 10:55:59] ERROR: Error-Response from https://app.module-loader.de/api.php
[2025-08-27 10:56:00] ERROR: Error sending the POST request: 

This PR adds an indicator on what could have gone wrong:

[2025-08-27 10:55:59] ERROR: Error-Response from https://app.module-loader.de/api.php
The OpenSSL PHP extension is required for https requests.
[2025-08-27 10:56:00] ERROR: Error sending the POST request: The OpenSSL PHP extension is required for https requests.

[RobinTheHood]

LGTM Thx 🥳