Make "Serve" command ENV whitelist more flexible

[rasmuscnielsen]

Issue

Currently the Artisan serve command filters out any host ENV variables that is not explicitly listed in a hardcoded array.

return in_array($key, [
    'APP_ENV',
    'LARAVEL_SAIL',
    'PHP_CLI_SERVER_WORKERS',
    'PHP_IDE_CONFIG',
    'SYSTEMROOT',
    'XDEBUG_CONFIG',
    'XDEBUG_MODE',
    'XDEBUG_SESSION',
]) ? [$key => $value] : [$key => false];

This is causing me quite a headache as I need to pass some additional ENV from docker-compose.yml using Sail. The additional ENV can be accessed just fine from CLI but will never be accessible from the browser because it is filtered out from the servecommand.

Specifically I need to pass a PORT_PREFIX from my host-machine that will be used to generate some URLs for other docker services running. This is only necessary in development context.

Proposal

Make it easier to allow extra ENV to be passed through to the php built-in server, either by

1. Passing through any ENV variable starting with a prefix such as PUBLIC_*. This is similar to what VUE CLI does by making any ENV variables accessible from client javascript if they start with VUE_APP_*. This would give the best developer experience as no customisations are needed by the developer.
2. Extracting the above whitelist to a public static $whitelist variable so it can be changed from a ServiceProvider@register function without having to extend and customise the serve command.

[rasmuscnielsen]

Implemented in #42444