Add support for credential based managed identity

[gladjohn]

Implement MSI V2 with /credential endpoint, ensuring robust token acquisition, SLC revocation handling, and probe logic for VM/VMSS environments.

Key Deliverables
MSI V2 /credential Endpoint Implementation

• Develop a design document detailing the token acquisition process for MSI V2.
• Include certificate handling procedures and source detection logic.
• Ensure clear documentation for SDK developers on integrating the /credential endpoint.
• Short-Lived Credential (SLC) Revocation Specification
• Define a structured approach for handling SLC revocation scenarios.
• Outline the process for acquiring new credentials when an existing one is revoked or expires.
• Ensure proper handling of revocation-related failures and retry mechanisms.
• VM/VMSS Credential Endpoint Probe Logic

Implement and document the probe logic for detecting the MSI V2 /credential endpoint in IMDS.

• Address scenarios related to IMDS restarts and expected response handling.
• Provide guidance on how SDKs should interpret probe results and fallback strategies.

Success Criteria

• Comprehensive documentation and design specifications are available for developers.
• Clear and actionable steps for integrating MSI V2 /credential endpoint, SLC revocation, and probing logic.
• Validation of probe logic ensuring seamless integration in VM/VMSS environments.