Added M3 functionality for User Management, added Keycloak security

Summary

• Added M3 functionality for User Management
• fixed some mistakes in user management, added pagination
• added Keycloak security
• added configuration files to work with keycloak
• added .env variables
• added readme explaning how to use keycloak
• modified tests to work with keycloak in user management
• modified application.yml files in all microservices with keycloak configurations

Test cases proposition

• tests in other microservices need to be modified to work with keycloakA

Closes #15 (closed)