More robust application of access permissions (#5062)

* More robust application of access permissions
We were in particular missing directory traversal `+X` in our current recommendations.
Extracted to own shell script so it can easily be invoked.
Update access permissions in Docker to account to be more robust.
#fix https://github.com/FreshRSS/FreshRSS/discussions/5037

* Minor simplification

* Restrict mkdir permissions
Default mkdir permissions are 0777, which is not good for security, so downgrade to 0770.

app/Controllers/userController.php

@@ -242,7 +242,7 @@ class FreshRSS_user_Controller extends FreshRSS_ActionController {
 		}
 		if ($ok) {
 			if (!is_dir($homeDir)) {
-				mkdir($homeDir);
+				mkdir($homeDir, 0770, true);
 			}
 			$ok &= (file_put_contents($configPath, "<?php\n return " . var_export($userConfig, true) . ';') !== false);
 		}