problem of current edge request and internal request determination

[wbpcode]

Title: problem of exist edge request and internal request determination

Description:

This is a feature has almost same lifetime with the Envoy self. But I think there are some problem in this feature:

1. A request will be determined as edge request only when the use_remote_address is enabled. But today, the original_ip_detection_extensions may be used as alternative of use_remote_address.
2. If there are multiple hop proxies and use_remote_address is used, the requests will always be treated as external requests except in the first hop.
3. If use_remote_address is used in a inner proxy, some requests may be determined as edge request incorrectly.

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Any extra documentation required to understand the issue.

[wbpcode]

I think may be an explicit flag to tell if the envoy is front envoy or not would be better. And use the internal_address_config as the unique approach to determine whether a request is trust request. (The allow_trusted_address_checks flag just make things more complex and hybrid the original ip dectection and trust ip detection. Considering the #36643, I didn't see the value of that.)

[wbpcode]

I know it may be impossible or very hard to change this, because this feature has very very long history. But anyway, I record its problems here for discussion or reference.

[wbpcode]

cc @mattklein123

[KBaichoo]

cc @alyssawilk