Add pub/get.php worker shim (issues #2, #3)

Ships the missing third pub-dir worker shim alongside pub/index.php
(App\Http) and pub/static.php (App\StaticResource), routing media
on-demand processing through the FrankenPHP worker pool instead of a
fresh per-request Magento bootstrap.

  pub/get.php
    -> \$frankengento = \Opengento\Application\App\Media::class;
    -> include 'worker.php';

The Media app implementation lands in the companion PR at
opengento/magento2-application (see PR description for the link).

composer.json
-------------
  - Adds pub/get.php to extra.map so the file is copied into the
    project's pub/ directory at install time (same mechanism as the
    existing index.php and static.php entries).
  - Bumps the require constraints to match the PHP 8.4+ / Magento 2.4.8+
    support matrix:
      php:                                  (new) ^8.4
      magento/magento2-base:                *  -> ^2.4.8
      opengento/module-application:         >=0.5 -> >=0.7
    The >=0.7 bump assumes opengento/module-application releases a 0.7
    after merging the companion PR. Tighten or loosen as appropriate
    once the version is published.

Closes #2 and #3.

Author: Alexandre Courtiol

composer.json

@@ -52,6 +52,10 @@
             [
                 "pub/static.php",
                 "pub/static.php"
+            ],
+            [
+                "pub/get.php",
+                "pub/get.php"
             ]
         ]
     }

pub/get.php

@@ -0,0 +1,10 @@
+<?php
+/**
+ * Copyright © OpenGento, All rights reserved.
+ * See LICENSE bundled with this library for license details.
+ */
+declare(strict_types=1);
+
+$frankengento = \Opengento\Application\App\Media::class;
+
+include 'worker.php';