Merge pull request from GHSA-mhr8-7rvg-8r43

* Prevent possible XSS attack vector on add_client
Update JS code to prevent possible XSS vector

Co-authored-by: Harold Kim <root@stypr.com>
Signed-off-by: Adam Warner <me@adamwarner.co.uk>

* Fix both addClient and deleteClient to prevent XSS

Signed-off-by: Harold Kim <root@stypr.com>

Co-authored-by: Harold Kim <root@stypr.com>

scripts/pi-hole/php/groups.php

@@ -347,6 +347,8 @@ if ($_POST['action'] == 'get_groups') {
         }
 
         foreach ($ips as $ip) {
+            // Encode $ip variable to prevent XSS
+            $ip = htmlspecialchars($ip);
             // Silently skip this entry when it is empty or not a string (e.g. NULL)
             if(!is_string($ip) || strlen($ip) == 0) {
                 continue;