Always use HTTP/2 preface for H2C

[ikhoon]

Motivation:

There are two modes to negotiate cleartext HTTP/2 connections. They are HTTP/2 connection preface and HTTP/1 upgrade requests. The default behavior is determined by ClientFactoryOptions.useHttp2Preface(). This option affects' http' and h2c, so even if a user uses h2c with prior knowledge, an upgrade request will be sent if useHttp2Preface() == false.

With prior knowledge, it is an unwanted behavior for useHttp2Preface() option to affect h2c scheme. h2c is an explicit scheme whose negotiation should be fixed to the HTTP/2 connection preface. Its endpoint may not understand the HTTP/1 upgrade.

So it would make more sense to apply to useHttp2Preface() option to adjust the default behavior of http. If both http and h2c follow useHttp2Preface(), there is no difference in behavior between them.

Modifications:

• Always use HTTP/2 connection preface for h2c
• useHttp2Preface() option now affects only http.

Result:

Armeria client always uses HTTP/2 connection preface for h2c, regardless of the value of useHttp2Preface().

[github-actions[bot]]

🔍 Build Scan® (commit: 5b58ffc9801ef126ed8443efc459630b6a1cc9e8)

Job name	Status	Build Scan®
build-windows-latest-jdk-21	✅	https://ge.armeria.dev/s/j3gikcrioleju
build-self-hosted-unsafe-jdk-8	✅	https://ge.armeria.dev/s/usav7bpli365k
build-self-hosted-unsafe-jdk-21-snapshot-blockhound	✅	https://ge.armeria.dev/s/se6bkbt67sz5k
build-self-hosted-unsafe-jdk-17-min-java-17-coverage	✅	https://ge.armeria.dev/s/ejljkwjlqh5rq
build-self-hosted-unsafe-jdk-17-min-java-11	✅	https://ge.armeria.dev/s/utsg2vd5agfxo
build-self-hosted-unsafe-jdk-17-leak	✅	https://ge.armeria.dev/s/uo7pojfp446je
build-self-hosted-unsafe-jdk-11	✅	https://ge.armeria.dev/s/4ey3cyvciubhm
build-macos-12-jdk-21	✅	https://ge.armeria.dev/s/vrxwblc4tghkc

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@ikhoon 👍 👍 👍