Add Fritz!Box plugin entry to docs/PLUGINS.md

The FRITZBOX plugin was not listed in the central plugin registry at
docs/PLUGINS.md. Requested by reviewer jokob-sk in PR #1592.

Changes:
- Add FRITZBOX entry to the Available Plugins table (docs/PLUGINS.md:60)
  Inserted alphabetically between FREEBOX and ICMP, with type 🔍
  (device_scanner) and a link to the plugin directory.

Author: sebingel

docs/PLUGINS.md

@@ -57,6 +57,7 @@ Device-detecting plugins insert values into the `CurrentScan` database table.  T
 | `DHCPSRVS`      | [dhcp_servers](https://github.com/netalertx/NetAlertX/tree/main/front/plugins/dhcp_servers/)                       | ♻        | DHCP servers                              |          |          |
 | `DIGSCAN`       | [dig_scan](https://github.com/netalertx/NetAlertX/tree/main/front/plugins/dig_scan/)                               | 🆎       | Dig (DNS) Name resolution                 |          |          |
 | `FREEBOX`       | [freebox](https://github.com/netalertx/NetAlertX/tree/main/front/plugins/freebox/)                                  | 🔍/♻/🆎  | Pull data and names from Freebox/Iliadbox |          |          |
+| `FRITZBOX`      | [fritzbox](https://github.com/netalertx/NetAlertX/tree/main/front/plugins/fritzbox/)                                | 🔍       | Fritz!Box device scanner via TR-064       |          |          |
 | `ICMP`          | [icmp_scan](https://github.com/netalertx/NetAlertX/tree/main/front/plugins/icmp_scan/)                             | ♻        | ICMP (ping) status checker                |          |          |
 | `INTRNT`        | [internet_ip](https://github.com/netalertx/NetAlertX/tree/main/front/plugins/internet_ip/)                         | 🔍       | Internet IP scanner                       |          |          |
 | `INTRSPD`       | [internet_speedtest](https://github.com/netalertx/NetAlertX/tree/main/front/plugins/internet_speedtest/)           | ♻        | Internet speed test                       |          |          |