Proxy: Support proxy server for SRS. v7.0.16 #3595

Job	Run time
multiple-arch-aarch64	22m 44s
cygwin64-cache	1m 42s
utest-regression-blackbox-test	9m 33s
multiple-arch-armv7	22m 6s
fast	1s
cygwin64	14m 51s
build-ubuntu20	3m 34s
build-centos7	5m 14s
build-cross-arm	5m 23s
build-ubuntu16	3m 5s
build-ubuntu18	3m 8s
build-cross-aarch64	5m 8s
coverage	3m 36s
multiple-arch-amd64	2m 30s
test-done	1s
	1h 42m 36s

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