Additional example apps

There is currently [one very basic example app](https://github.com/ccouzens/keycloak-openapi/tree/main/example_app), written in nodejs that gets a list of clients.

It would be good to have more example apps.

The examples can do more, or they could be written in a different language or framework.

The examples can be part of this repo, or they can be linked off to another repo if that's the preference of the contributor.

It would be good for any examples to have usage instructions, especially if they're using a language or tooling I'm not familiar with.

Start by inspecting the existing example_app and its current usage instructions. Decide which additional example scope and language or framework are appropriate, then add the example in this repository or link to an external repository. Done means the example demonstrates useful usage and includes clear setup and usage instructions.

Written by the indexing model from the issue text.