BackendTLSPolicy does not support ServiceImport backends

[muwaqar]

Description:
I am going through the processDestination() code (linked below) and I see BackendTLSPolicy handling for Service and Backend destinations only. Seems there is no ds.TLS set for ServiceImport backends.

https://github.com/confluentinc/envoy-gateway/blob/main/internal/gatewayapi/route.go#L1270

Is this deliberate or an oversight?

Repro steps:
N/A

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Environment:

Include the environment like gateway version, envoy version and so on.

Logs:

Include the access logs and the Envoy logs.

[nareddyt]

(after this is fixed) we should update the diagram in https://gateway.envoyproxy.io/docs/concepts/concepts_overview/ to reflect that BackendTLSPolicy can target a ServiceImport