FrankenPHP: Allow running Octane without artisan command

[AlliBalliBaba]

This PR is the minimum required to run Octane without pcntl and the artisan octane wrapper process.

Through a discussion in the FrankenPHP repo we realized that when working with a Laravel app that was embedded as a binary, the embedded repository path gets apparently lost along the way, preventing worker mode from working properly.

One way of circumventing this is by starting the process directly through an embedded Caddyfile with frankenphp run or frankenphp php-server. This PR sets sensible defaults for APP_BASE_PATH, APP_PUBLIC_PATH and MAX_REQUESTS, therefore allowing to run the frankenphp-worker.php script independently from php artisan octane:start.

This will not affect the current behavior for users using php artisan octane:start or php artisan octane:frankenphp.