add service discovery for alertmanager #18

Job	Run time
UI tests	3m 9s
golangci-lint	4m 50s
Go tests	4m 55s
Go tests with previous Go version	4m 36s
Build Prometheus for common architectures (0)	4m 49s
Build Prometheus for common architectures (1)	4m 47s
Mixins tests	3m 42s
Go tests on Windows	16m 20s
Build Prometheus for common architectures (2)	4m 49s
Build Prometheus for all architectures	0s
fuzzing	0s
codeql / Analyze (go)	9m 50s
codeql / Analyze (javascript)	2m 37s
Publish UI on npm Registry	1m 52s
Publish release artefacts	0s
Publish main branch artifacts	0s
	1h 6m 16s

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