change: use apisix.enable_http2 to enable HTTP/2 in APISIX #12826

Job	Run time
run ci on centos7 (lua-resty-worker-events, t/plugin/[a-k]*)	31m 28s
run ci on centos7 (lua-resty-worker-events, t/plugin/[l-z]*)	31m 34s
run ci on centos7 (lua-resty-worker-events, t/admin t/cli t/config-center-yaml t/control t/core t...	25m 17s
run ci on centos7 (lua-resty-worker-events, t/node t/pubsub t/router t/script t/secret t/stream-n...	21m 49s
run ci on centos7 (lua-resty-events, t/plugin/[a-k]*)	32m 6s
run ci on centos7 (lua-resty-events, t/plugin/[l-z]*)	32m 52s
run ci on centos7 (lua-resty-events, t/admin t/cli t/config-center-yaml t/control t/core t/debug ...	23m 47s
run ci on centos7 (lua-resty-events, t/node t/pubsub t/router t/script t/secret t/stream-node t/u...	21m 44s
	3h 40m 37s

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