docs(client mgmt): create documentation for client scripts

## General Guidelines

- Start by covering the general definition of the feature in a few lines and then point to the appropriate section of the SPEC. Please refrain from repeating what is there in the SPEC already.
- Try to make the content Janssen Server specific ( e.g. what are the related Janssen Server properties or feature flags, how to change relevant settings using TUI/command line (use the screenshots), recommendations around recommended values, use-cases)
- Follow the [documentation contribution guidelines](https://docs.jans.io/head/CONTRIBUTING/).
- Feel free to refer to content available in Gluu documentation (or any other IDP) if the content doesn't need to be customized for Janssen Server

## Document Location

https://docs.jans.io/head/admin/auth-server/client-management/client-scripts/

## Suggested sections