WHMCS 8.6 and PHP 8.1 support

[truffiere]

Problem/Motivation

WHMCS have just released PHP 8.6 RC which requires PHP 8.1 and doesn not support PHP 7.x

Proposed resolution

Update the module/create a PHP 8.1 version

Repeatable

Always

(If it is a bug, you are reporting lease specify:)

Steps to repeat: (Describe how the issue can be repeated by someone who is to work on it)

1. Step 1
2. Step 2
3. ...

Expected Results:

(What you expected steps 1, 2 and 3 to give)

Actual Results:

(What is gave including any error messages, memory dump etc that can help)