Update php to 8.1.0

[shivammathur]

php formula has been upgraded to stable 8.1.0.

• Now you can install PHP 8.1 using

brew install shivammathur/php/php

or using the php@8.1 Alias

brew install shivammathur/php/php@8.1

• To install php@8.0, please use the php@8.0 formula.

brew install shivammathur/php/php@8.0

Progress

• Update php.rb formulae to 8.1.0.
• Update php alias to php@8.1.rb.
• Remove php@8.1 formula.
• Add PHP 8.0 back as php@8.0 formula.
• Update docs.