Require PHP >= 8.1.0

[MauricioFauth]

Adds a check for the minimum required PHP version. As enumerations are used, at least PHP 8.1 is required. It's also the required version for PhD.

[alfsb]

This ideia is good, but way over enginered. But please leave these two PRs open, white I try to cook something more simple with PHP_VERSION and PHP_BINARY.

[MauricioFauth]

This ideia is good, but way over enginered.

I agree.

But please leave these two PRs open, white I try to cook something more simple with PHP_VERSION and PHP_BINARY.

Okay.

[hakre]

I'm undecided whether this is nice to have or only a maintenance burden, however as some food for thought: I think it would be of benefit when a version check is implemented, that the existing --version flag output pattern and behaviour is preserved.