Add Workload Identity Federation for SCIM Provisioning documentation (#130)

Add comprehensive markdown guide covering:
- WIF overview and JWT Bearer Assertion flow (RFC 7523)
- 3-step admin configuration flow for Entra Portal
- JWT claims reference with example token payload
- ISV requirements for JWKS validation and token issuance
- SAP SuccessFactors integration example
- FAQ for key caching, rotation, and fallback
- Security considerations and legacy vs WIF comparison

Co-authored-by: Jeevan Desarda <jeevansd@gmail.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: 3 people