Fix Runtime Error for API Invocation with Security Set to 'None' When Production Endpoint is Missing

[ashanhr]

Purpose

• Invoking an API resource with security set to 'None' returns a runtime error if the Production endpoint is not configured, even though the request can be routed to the Sandbox endpoint. This PR addresses and resolves this issue.
• Add tests to validate the flows in Velocity templates when resource security is set to None.
• Related to: Runtime Error When Unmarking Production Endpoint and Disabling Security on API Resource api-manager#3294

Approach

• Updated the Velocity template to properly handle resources when security is set to 'None'.
• Tested all possible scenarios across the Hybrid, Sandbox, and Production environments to ensure the fix resolves the issue without impacting other functionalities.
• Add two tests for the hybrid gateway environment and the sandbox gateway environment,
  • In the hybrid gateway environment, the following scenarios are tested:
    • Both production and sandbox endpoints are available.
    • Only the production endpoint is available.
    • Only the sandbox endpoint is available.
  • In the sandbox gateway environment, the following scenarios are tested:
    • Both production and sandbox endpoints are available.
    • Only the sandbox endpoint is available.