fix: use max_req_body_bytes field in custom_format (#11771) #17133

Job	Run time
build (ubuntu-20.04, linux_openresty, lua-resty-worker-events, t/plugin/[a-k]*)	36m 15s
build (ubuntu-20.04, linux_openresty, lua-resty-worker-events, t/plugin/[l-z]*)	34m 13s
build (ubuntu-20.04, linux_openresty, lua-resty-worker-events, t/admin t/cli t/config-center-yaml...	24m 55s
build (ubuntu-20.04, linux_openresty, lua-resty-worker-events, t/node t/pubsub t/router t/script ...	26m 0s
build (ubuntu-20.04, linux_openresty, lua-resty-events, t/plugin/[a-k]*)	34m 50s
build (ubuntu-20.04, linux_openresty, lua-resty-events, t/plugin/[l-z]*)	34m 29s
build (ubuntu-20.04, linux_openresty, lua-resty-events, t/admin t/cli t/config-center-yaml t/cont...	25m 25s
build (ubuntu-20.04, linux_openresty, lua-resty-events, t/node t/pubsub t/router t/script t/secre...	28m 24s
	4h 4m 31s

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