feat(keycloak_saml_client_installation_provider): support zip files

[Codelax]

Currently, the documentation makes use of saml-idp-descriptor provider to fetch the saml xml.
This provider seems not existent in the current version of keycloak.
I found a valid xml with the mod-auth-mellon provider but the returned value is a zip file.

This zip file is currently being put in value attribute as string, as this is binary data, it breaks the file and we cannot use it in terraform. An easy fix would be to add a value_base64 attribute but it would still remain hard to use as terraform does not provide a way to interact with a zip. We also could create a terraform function to help handle this zip file but it requires the terraform framework rather than the old SDK.

I added a new zip_files map attribute that will contain all files contained in the zip.