Add missing parameter to on_http_response_trailers

[casimiro]

Proxy wasm spec defines proxy_on_http_trailers as a 3 parameter function: context_id, num_trailers, end_of_stream. This PR adds the missing end_of_stream parameter.

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[PiotrSikora]

Hi @casimiro, apologies for the late response, and thanks for the contribution!

The current code is fine (otherwise, it wouldn't work with the existing host implementations). The issue is that there is no written specification for the Proxy-Wasm ABI v0.2.1, which is implemented by Envoy, MSON and all the SDKs (but writting it down is my primary task for the next 2 weeks).

Where did you run into this issue?

[casimiro]

Hi @PiotrSikora, I apologize for the ultra late response! I ran into this when experimenting with adding http trailers support to ngx_wasm_module. I assumed the end_of_stream argument was missing based on the late vNEXT spec which included end_of_stream as part of proxy_on_http_response_trailers.

Thank you for the response.