Fix: Remove intentional error injection causing NullPointerException in appointment service

[github-actions]

Problem

The appointment-service-get Lambda function was experiencing critical availability issues with 475 NullPointerException errors in the last 4+ hours, causing:

• High error rate (~2 errors/minute)
• API Gateway latency degradation (677ms p99 for /list, 282ms for /get)
• Cascade effects on downstream services

Root Cause

Intentional error injection in lambda-petclinic/sample-apps/function3-different-version/lambda_function.py at line 27:

if pet_id == "111111111111":
    raise Exception('Fail to parse the request. Cause: NullPointerException')

This was triggered by the HttpRequesterFunction (function4) running every minute via EventBridge, which generates malicious requests by replacing petid=dog with petid=111111111111.

Solution

• ✅ Removed the intentional exception throwing logic
• ✅ Maintains proper error handling for missing parameters
• ✅ Preserves all other functionality and validation

Impact

This fix will:

• Eliminate the 475+ recurring exceptions
• Reduce API Gateway latency back to normal levels
• Stop the cascade effect on downstream services
• Maintain proper Application Signals observability without artificial errors

Testing

The fix removes only the problematic error injection while preserving:

• Parameter validation for owners and pet_id
• Proper error responses for missing recordId
• DynamoDB error handling
• OpenTelemetry tracing functionality

Resolves the critical availability issues identified in the Application Signals investigation.