[Installer] Enhance Support for Debian & Ubuntu Old Version

[Edi Septriyanto]

LEMPer Stack Debian support is experimental!

If you are using Debian stable versions, stretch and buster, it should work properly.

But, to support latest and old version, there are some glitches..

1. Nginx & PHP requires alternative repository for backward compatibility with old Debian jessie (and Ubuntu xenial) version which is not supported by Ondrej's repo, while the latest version bullseye is already available.
2. PHP also requires alternative installation method (from source) which is currently absence.

PS. Installing from source is not the best solution and not recommended for low-end box server, but this is currently the most possible approach.

[Edi Septriyanto]

Compile PHP from source, example

https://php.watch/articles/compile-php-ubuntu