fix: Fortinet Radius script and documentation

**Describe the bug**
Jans has [Fortinet Radius interception script](https://github.com/JanssenProject/jans/blob/main/docs/script-catalog/person_authentication/other/fortinet/FortinetExternalAuthenticator.py) and the [document](https://github.com/JanssenProject/jans/blob/main/docs/script-catalog/person_authentication/other/fortinet/README.md) to go with it.

Both needs updates:

- For script: Check if the script is relevant to Jans and working
- For README: README talks about Gluu server and how to configure. If the script is Gluu server specific, move the documentation and script out of Jans. If it is relevant to jans, update the README to focus on Jans. And create a separate issue for Gluu server to create doc there as well.