Upgrade to PHP 8.1.5

Summary:
PHP 8.1 will allow to build tools and CI images with recent interpreter.

Bump Oniguruma version to 6.9.8.

Reference: https://www.php.net/ChangeLog-8.php#8.1.5

Ref T1725

Test Plan:
docker build .
docker run -it --rm hashnbr bash
php -i => and check if everything is okey

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1725

Differential Revision: https://devcentral.nasqueron.org/D2678