Mark objected as deleted (untracked) in LKG

[jkeane]

Type of PR

• [ ] Documentation changes
• [X] Code changes
• [X] Test changes
• [ ] CI-CD changes
• [ ] GitHub Template changes

Purpose of PR

Add feature: when SP is found in discovery and is removed, then update its tracking record in LKG if it exists. Added unit tests for ServicePrincipalProcessor::DiscoverDeltas

Review notes

Issues Closed or Referenced

• Closes #543