Refactor module to remove dependency on Keycloak libraries

[AFaust]

The Keycloak Java libraries referenced / used in this module have been deprecated for a while and starting in Keycloak 25, they are no longer updated/released by the Keycloak project.
This module should be refactored (potentially from the ground up) to remove this dependency. In the process, the refactoring should also aim to make the project independent from Keycloak in other aspects, i.e. by supporting other (generic) OIDC Identity Providers apart from Keycloak.

[willisplummer]

Related to this, I've been running into a bug where the keycloak GroupRepresentation doesn't account for the sometimes present subGroupCount field.

alfresco_1            | 2025-01-08T05:15:00.474756547Z Caused by: com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "subGroupCount" (class de.acosix.alfresco.keycloak.deps.keycloak.representations.idm.GroupRepresentation), not marked as ignorable (8 known properties: "clientRoles", "subGroups", "path", "attributes", "id", "realmRoles", "access", "name"])

Hope this is helpful!

Note: I think this is causing group sync to fail for me