feat: added alertmanager client package #1818

Job	Run time
Lint golang code	15s
Run go tests	1m 12s
End-to-End test with kured with code and manifests from HEAD (command) (1.27)	17m 26s
End-to-End test with kured with code and manifests from HEAD (concurrent) (1.27)	11m 43s
End-to-End test with kured with code and manifests from HEAD (command) (1.28)	18m 23s
End-to-End test with kured with code and manifests from HEAD (signal) (1.27)	18m 44s
End-to-End test with kured with code and manifests from HEAD (concurrent) (1.28)	12m 33s
Check docs for incorrect links	6s
End-to-End test with kured with code and manifests from HEAD (command) (1.29)	16m 40s
End-to-End test with kured with code and manifests from HEAD (signal) (1.28)	16m 40s
End-to-End test with kured with code and manifests from HEAD (concurrent) (1.29)	10m 50s
End-to-End test with kured with code and manifests from HEAD (signal) (1.29)	12m 44s
Lint bash code with shellcheck	5s
Build image and scan it against known vulnerabilities	1m 29s
	2h 18m 50s

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