Add external claim mapper extension to extensions page

[zloom]

Hello, keycloak maintainers!

I developed extension and would like to propose to include it to https://www.keycloak.org/extensions. It is almost same as https://github.com/groupe-sii/keycloak-json-remote-claim
I made couple of improvements.

• Added user token auth, jsonpath transform and some other configurations, including all features from JSON Remote claim Mapper for Keycloak
• Tested with last keycloak release 25.0.0
• Repository contains all test tools including remote api stub, that helped me alot during debugging my keycloak integration.

I was really enjoying using keycloak in my projects, so i would like to contribute to it. Please take a look.

[ahus1]

Thank you for this extension! It should be available online soon.

I see that it is currently MIT licensed. Keycloak and a lot of extensions are Apache 2 based, which allows to borrow code from other extensions and and Keycloak code as well. So I'd suggest to change the license of your plugin to match the Keycloak license - still this is totally up to you if you choose to do that.