add sum connector #48

Job	Run time
setup-environment	1m 40s
generate-metrics	4m 44s
coverage	8m 12s
gofmt	4m 25s
cross-compile (binaries-darwin_amd64)	4m 28s
lint	13m 50s
cross-compile (binaries-darwin_arm64)	4m 42s
test	14m 10s
cross-compile (binaries-linux_amd64)	4m 32s
tidy	1m 18s
cross-compile (binaries-linux_arm64)	4m 24s
cross-compile (binaries-windows_amd64)	4m 24s
cross-compile (binaries-linux_ppc64le)	4m 29s
	1h 15m 18s

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