fix(patchs): fix kong.request.enable_buffering PDK function cannot be used when dowstream uses HTTP/2.

[oowl]

Summary

1. kong.request.enable_buffering PDK function can work fine when downstream using HTTP/2, which also means all of the kong plugins including the response function phase now work in HTTP2 protocol.
2. Remove http2 hardcode limitation in ngx.location subrequest API by patch bugfix: remove http2 hardcode limitation in ngx.location subrequest API openresty/lua-nginx-module#2355
3. Extend kong test helpers function helpers.proxy_ssl_client and helpers.proxy_clien http2 protocol support by https://github.com/oowl/lua-reqwest
4. Improve some of the http2 downstream protocol tests in our test cases. eg: spec/03-plugins/38-ai-proxy/* and spec/02-integration/05-proxy/24-buffered_spec.lua

Checklist

• The Pull Request has tests
• A changelog file has been created under changelog/unreleased/kong or skip-changelog label added on PR if changelog is unnecessary. README.md
• There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

Issue reference

AG-108
FTI-5725

[bungle]

@oowl what has been upstream answer to this? I guess they ended up adding it at some point (the limitation), but have it been changed there since? What are the unknowns?

[bungle]

Ok, I see: openresty/lua-nginx-module#2243 and openresty/lua-nginx-module#2355

[bungle]

@oowl can you also check your example with SSL/TLS connection just to be sure (it is rather pointless to do h2 without SSL/TLS):
openresty/lua-nginx-module#2243 (comment)

[oowl]

@oowl can you also check your example with SSL/TLS connection (it is rather pointless to do h2 without SSL/TLS): openresty/lua-nginx-module#2243 (comment)

Yeah, I will.
I will also complement some http2-related tests in our plugin and pdk integration test to verify that this patch works fine in our case. Let's wait for my good news

[bungle]

Just some comments. I like this a lot if it works! Good work on reqwest too!

[oowl]

Once it got 2 approved. I will squash my commit to 3 separate commits that can be merged by the rebase and merge button.

[bungle]

Looks good!