Add http2 feature #1731

Job	Run time
Check Style	5s
unstable features	5s
MSRV	4m 51s
linux / nightly	1m 16s
Android	21s
WASM	43s
linux / stable	39s
linux / beta	48s
macOS / stable	1m 44s
windows / stable-x86_64-msvc	3m 44s
windows / stable-i686-msvc	4m 49s
windows / stable-x86_64-gnu	6m 54s
windows / stable-i686-gnu	7m 20s
feat.: default-tls disabled	45s
feat.: rustls-tls	44s
feat.: rustls-tls-manual-roots	46s
feat.: rustls-tls-native-roots	52s
feat.: native-tls	46s
feat.: default-tls and rustls-tls	47s
feat.: cookies	52s
feat.: blocking	54s
feat.: gzip	55s
feat.: brotli	56s
feat.: deflate	50s
feat.: json	49s
feat.: multipart	48s
feat.: stream	41s
feat.: socks/default-tls	44s
feat.: socks/rustls-tls	51s
feat.: trust-dns	51s
Docs	1m 37s
CI is green	1s
	48m 48s

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