Addition of TLSRoute with Terminate mode conformance tests

[mlavacca]

What would you like to be added:

Conformance tests for TLSRoutes with TLS terminate mode.

Why this is needed:

GEP-2907 update listed the TLS modes supported by each protocol. Since we need to support both Passthrough and Terminate TLS mode for TLSRoute, we want to add conformance tests for both of them. #1579 already tracks conformance tests for TLSRoutes with Passthrough, while this issue aims at tracking conformance tests for TLSRoutes with Terminate mode.