Conformance Tests for ResolvedRefs Condition in BackendTLSPolicy

[snorwin]

Following the implementation of the ResolvedRefs condition for the BackendTLSPolicy (#3992) add conformance tests to verify correct status reporting across implementations.

Proposed Test Cases:

• All CACertificateRefs resolve successfully → ResolvedRefs=True and Accepted=True
• Missing or misconfigured CA certificate objects → ResolvedRefs=False with Reason=InvalidCACertificateRef and Accepted=True
• Unsupported Group/Kind → ResolvedRefs=False with Reason=UnsupportedFeature and Accepted=True
• No CACertificateRefs can be resolved → ResolvedRefs=False and Accepted=False with Reason=NoCACertificates