Refactor Workflow Tests and Services to Use System.Text.Json

[reeshika-h]

• Updated WorkflowTest.cs to replace Newtonsoft.Json with System.Text.Json for JSON handling.
• Modified assertions in tests to utilize OpenJsonObjectResponse instead of OpenJObjectResponse.
• Changed BulkWorkflowUpdateServiceTest to use System.Text.Json for serialization settings.
• Refactored Workflow.cs and WorkflowModel.cs to remove Newtonsoft.Json dependencies and implement System.Text.Json attributes.
• Ensured consistency in JSON serialization options across the codebase.

[github-actions]

🔒 Security Scan Results

ℹ️ Note: Only vulnerabilities with available fixes (upgrades or patches) are counted toward thresholds.

Check Type	Count (with fixes)	Without fixes	Threshold	Result
🔴 Critical Severity	0	0	10	✅ Passed
🟠 High Severity	0	0	25	✅ Passed
🟡 Medium Severity	0	0	500	✅ Passed
🔵 Low Severity	0	0	1000	✅ Passed

⏱️ SLA Breach Summary

✅ No SLA breaches detected. All vulnerabilities are within acceptable time thresholds.

Severity	Breaches (with fixes)	Breaches (no fixes)	SLA Threshold (with/no fixes)	Status
🔴 Critical	0	0	15 / 30 days	✅ Passed
🟠 High	0	0	30 / 120 days	✅ Passed
🟡 Medium	0	0	90 / 365 days	✅ Passed
🔵 Low	0	0	180 / 365 days	✅ Passed

✅ BUILD PASSED - All security checks passed

[OMpawar-21]

LGTM