Add remote requirements checking to upgrade.php

quoted from #14127
    There is a race condition in the upgrade.php file where it can't
    currently know the hard requirements for the version it's upgrading to
    until it does a git pull. By that time, it will have pulled new source
    code that possibly relies on an incompatible version of php, leaving you
    with a broken installation.

    Example: You're running v6.2.x on PHP 7.4, which is fine. v7 requires
    PHP 8.1 or 8.2, but we couldn't know that when we released v6. or v5 for
    that matter. We could change the requirements in the most-recent v6
    version of upgrade.php, but that doesn't help anyone who doesn't upgrade
    first to the most recent v6.

With this change, we implement fetching and incorporating the
requirements data from the remote file.

It's just fetching/decoding a couple of json values that replace the
hard-coded version requirements.

We move the branch checking higher than the php version checking so that
we can use the defined/overridden $branch to decide what branch to pull
the requirements from.

upgrade.php

@@ -1,8 +1,24 @@
 <?php
 (PHP_SAPI !== 'cli' || isset($_SERVER['HTTP_USER_AGENT'])) && die('Access denied.');
 
-$php_min_works = '7.4.0';
-$php_max_wontwork = '8.2.0';
+$app_environment = 'develop';
+
+// Check if a branch or tag was passed in the command line,
+// otherwise just use master
+(array_key_exists('1', $argv)) ? $branch = $argv[1] : $branch = 'master';
+
+
+// Fetching most current upgrade requirements from github. Read more here: https://github.com/snipe/snipe-it/pull/14127
+$remote_requirements_file = "https://raw.githubusercontent.com/snipe/snipe-it/$branch/.upgrade_requirements.json";
+$upgrade_requirements = json_decode(file_get_contents($remote_requirements_file), true);
+
+if (! $upgrade_requirements) {
+    die("\nERROR: Failed to retrieve remote requirements from $remote_requirements_file\nExiting.\n\n");
+}
+
+$php_min_works = $upgrade_requirements['php_min_version'];
+$php_max_wontwork = $upgrade_requirements['php_max_wontwork'];
+// done fetching requirements
 
 
 if ((strtoupper(substr(PHP_OS, 0, 3)) === 'WIN') || (!function_exists('posix_getpwuid'))) {
@@ -17,12 +33,6 @@
 }
 
 
-$app_environment = 'develop';
-
-// Check if a branch or tag was passed in the command line,
-// otherwise just use master
-(array_key_exists('1', $argv)) ? $branch = $argv[1] : $branch = 'master';
-
 echo "--------------------------------------------------------\n";
 echo "WELCOME TO THE SNIPE-IT UPGRADER! \n";
 echo "--------------------------------------------------------\n\n";