h3: add support for additional HEADERS #5391

Job	Run time
quiche_ios (x86_64-apple-ios)	1m 10s
quiche_ios (aarch64-apple-ios)	1m 14s
quiche_macos (macos-13)	4m 18s
quiche	5m 24s
quiche_macos (macos-latest)	2m 5s
quiche_windows (x86_64-pc-windows-msvc)	5m 33s
quiche (boringssl-boring-crate)	4m 23s
quiche_windows (i686-pc-windows-msvc)	5m 11s
quiche (openssl)	6m 59s
quiche_windows (x86_64-pc-windows-gnu)	7m 13s
android_ndk_lts (aarch64-linux-android)	1m 9s
quiche_windows (i686-pc-windows-gnu)	5m 11s
android_ndk_lts (armv7-linux-androideabi)	1m 1s
docker	2m 11s
android_ndk_lts (x86_64-linux-android)	1m 5s
http3_test	44s
android_ndk_lts (i686-linux-android)	59s
nginx (1.16.1)	1m 11s
quiche_multiarch (aarch64-unknown-linux-gnu)	2m 58s
quiche_multiarch (armv7-unknown-linux-gnueabihf)	3m 23s
quiche_multiarch (i686-unknown-linux-gnu)	1m 57s
	1h 5m 19s

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