feat: allow configuring allow-headers in grpc-web plugin #1834

Job	Run time
run ci on redhat ubi (lua-resty-worker-events, t/plugin/[a-k]*)	30m 16s
run ci on redhat ubi (lua-resty-worker-events, t/plugin/[l-z]*)	28m 51s
run ci on redhat ubi (lua-resty-worker-events, t/admin t/cli t/config-center-yaml t/control t/cor...	22m 11s
run ci on redhat ubi (lua-resty-worker-events, t/node t/pubsub t/router t/script t/secret t/strea...	19m 42s
run ci on redhat ubi (lua-resty-events, t/plugin/[a-k]*)	29m 39s
run ci on redhat ubi (lua-resty-events, t/plugin/[l-z]*)	29m 12s
run ci on redhat ubi (lua-resty-events, t/admin t/cli t/config-center-yaml t/control t/core t/deb...	22m 3s
run ci on redhat ubi (lua-resty-events, t/node t/pubsub t/router t/script t/secret t/stream-node ...	21m 29s
	3h 23m 23s

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