feat: allow for global environment variables to be configured.

This leverages the existing `.valet-env.php` file capability, but just adds the Valet Home directory as a first-lookup location.

So, now Valet will check for `.valet-env.php` in:
- `~/.config/valet/`
- then the current project folder

Author: yCodeTech

cli/Valet/Drivers/ValetDriver.php

@@ -222,6 +222,10 @@ protected function isActualFile($path) {
 	 */
 	public function loadServerEnvironmentVariables($sitePath, $siteName) {
 		$varFilePath = "$sitePath/.valet-env.php";
+
+		if (!file_exists($varFilePath)) {
+			$varFilePath = VALET_HOME_PATH . '/.valet-env.php';
+		}
 		if (!file_exists($varFilePath)) {
 			return;
 		}