doc: add example for export metrics with prometheus and hyper #224

Job	Run time
run with single worker thread and deadlock detection	5m 1s
run with address saniziter	6m 1s
run with leak saniziter	5m 34s
check build with madsim	1m 41s
misc check	6s
rust ffmt check (ubuntu-latest)	32s
rust ffmt check (macos-latest)	13s
rust test with codecov (ubuntu-latest, stable)	11m 9s
rust ffmt check (windows-latest)	2m 9s
rust udeps test (ubuntu-latest)	6m 50s
rust test with codecov (ubuntu-latest, 1.82.0)	11m 7s
rust udeps test (macos-latest)	6m 27s
rust test with codecov (macos-latest, stable)	5m 30s
rust udeps test (windows-latest)	12m 32s
rust test with codecov (macos-latest, 1.82.0)	6m 29s
rust test with codecov (windows-latest, stable)	12m 12s
rust test with codecov (windows-latest, 1.82.0)	11m 30s
	1h 45m 3s

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