docs(adr): Add ADR 0003 - Access Management Clients

[vairav]

Summary

• Adds ADR 0003 documenting the access management client applications
• Describes the Management API, Web UI, and CLI tools for administrators
• Documents the architecture for user, role, and policy management

Changes

• Created new ADR 0003 for Access Management Clients
• Updated RFC index to include the new document
• Documents three client interfaces: REST API, Web UI, and CLI
• Includes integration with Keycloak for authentication

Components Documented

• Management API: REST API on port 3002 for user/role/policy operations
• Management UI: React-based web interface for administrators
• Management CLI: Command-line tool for scripting and automation

Key Topics Covered

• Authentication flow via Keycloak
• User and role management endpoints
• Policy viewing and audit capabilities
• CLI command reference

Test Plan

• Verify documentation renders correctly in Sphinx
• Review API endpoints against actual implementation
• Confirm CLI commands match implemented functionality