Add support in library to call other non-admin REST API calls

[sachingaikwad123]

My understanding is currently mantelo only supports calling 'admin' related REST APIs of Keycloak. From docs:

Once you have configured how to authenticate to Keycloak, the rest is easy-peasy. mantelo starts with the URL /admin/realms/ and constructs the URL from there, depending on how you call the client.

This is great! Apart from this, I think there is scope to support calling other REST API requests as well from mantelo. For example, for obtaining permissions, clients are expected to do such a POST call:

curl -X POST \
  http://${host}:${port}/realms/${realm}/protocol/openid-connect/token \
  -H "Authorization: Bearer ${access_token}" \
  --data "grant_type=urn:ietf:params:oauth:grant-type:uma-ticket" \
  --data "audience={resource_server_client_id}" \
  --data "permission=Resource A#Scope A" \
  --data "permission=Resource B#Scope B"

There should be a way in 'mantelo' to call such POST calls as well.

Note:

1. python-keycloak supports this with 'permission_check' function. But it used to lack passing 'claim_token' argument. Recently, python-keycloak fixed this problem universally by allowing to pass 'extra_payload' args. Checkout issue raised and how it was closed: permission_check: Add support to passing other optional params like claim_token  marcospereirampj/python-keycloak#619

2. I can provide steps to setup keycloak for configuration of authorization services feature, if required.