Index Claim Accessors

[mauesrog]

Problem: While accessible, index claims are hard to directly obtain from the IssuanceAttestationsModel.

Solution: Implement index claims accessors for both BaseAttestationModel and IssuanceAttestationsModel.

Validation: Full coverage unit tests of index claim accessors.

Type of change:

• [x] Feature work
• [ ] Bug fix
• [ ] Documentation
• [ ] Engineering change
• [ ] Test
• [ ] Logging/Telemetry

Risk:

• [ ] High – Errors could cause MAJOR regression of many scenarios. (Example: new large features or high level infrastructure changes)
• [ ] Medium – Errors could cause regression of 1 or more scenarios. (Example: somewhat complex bug fixes, small new features)
• [x] Small – No issues are expected. (Example: Very small bug fixes, string changes, or configuration settings changes)

Work Item links: https://identitydivision.visualstudio.com/Engineering/_workitems/edit/1059795

Documentation Links: https://microsoft.sharepoint.com/:w:/t/ProjectAspen/EZrgaKQGz1hAsEHIvbi_gkkBQAooRqiZIZMezd8D-QT3tQ?e=O1LrmZ