Expose authorize() and entitlement() from keycloak-authz.js in keycloak-js

[sreenath-n]

The methods authorize() and entitlement() present in keycloak-authz.js (which is part of keycloak-js) doesn't seem to be exposed in react-keycloak.

Refer the below documentation for more details:
https://www.keycloak.org/docs/latest/authorization_services/index.html#_enforcer_js_adapter