add service discovery for alertmanager #19

Job	Run time
Go tests	4m 54s
Go tests on Windows	16m 51s
Build Prometheus for common architectures (0)	4m 54s
golangci-lint	49s
Go tests with previous Go version	4m 49s
Mixins tests	3m 54s
UI tests	3m 35s
Build Prometheus for common architectures (1)	4m 54s
Build Prometheus for common architectures (2)	5m 12s
Build Prometheus for all architectures	0s
fuzzing	0s
codeql / Analyze (go)	11m 47s
codeql / Analyze (javascript)	2m 47s
Publish UI on npm Registry	1m 35s
Publish release artefacts	0s
Publish main branch artifacts	0s
	1h 6m 1s

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