Idea: Extend sanity checks

[BitcoinMitchell]

We already sanity check the PHP version and BTCPay Server version, but it might be smart to extend these checks even further.

Possible checks:

• Ensure that no relevant core classes are overwritten
• Ensure all expected PHP extensions are available to us
• Ensure that we have internet access
• Ensure a proper domain is configured
• Ensure HTTPS is configured (and potentially enforced)
  • HTTPS is required for the frontend controllers, so this is technically a must.

This could help decrease the amount of issue people have by showing them upfront what is wrong with their PrestaShop installation.