feat: migrate Environment and Global Field modules to System.Text.Json

[OMpawar-21]

Summary

Migrates Environment and Global Field modules from Newtonsoft.Json to System.Text.Json as part of the ongoing modernization effort.

Changes

• Migrate Environment and Global Field models to use System.Text.Json attributes
• Update service layer to use JsonSerializerOptions and modern serialization patterns
• Re-enable previously disabled modules in project configuration
• Ensure compatibility with existing STJ infrastructure

Technical Updates

• Replace legacy JSON attributes with System.Text.Json equivalents
• Update service constructors and serialization methods
• Maintain API compatibility and existing interfaces
• Follow established patterns from previous migrations

Benefits

• Improved performance with System.Text.Json
• Reduced dependency on legacy Newtonsoft.Json package
• Consistent serialization approach across the SDK
• Better integration with modern .NET ecosystem

Testing

• All modules build successfully
• No breaking changes to public APIs
• Maintains backward compatibility

[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

[sunil-lakshman]

LGTM