Add parameter `alerts.excludeNamespaces` to exclude specific namespaces from base alerts #488

Job	Run time
linting (lint_jsonnet)	5s
linting (lint_yaml)	8s
test (capacity-alerts)	1m 30s
linting (lint_adoc)	23s
golden (capacity-alerts)	1m 24s
test (release-4.11)	1m 11s
editorconfig	6s
test (remote-write)	1m 5s
golden (release-4.11)	1m 10s
test (user-workload-monitoring)	1m 6s
golden (remote-write)	1m 11s
test (capacity-alerts-with-node-labels)	1m 41s
golden (user-workload-monitoring)	1m 7s
test (vsphere)	1m 11s
golden (capacity-alerts-with-node-labels)	1m 7s
test (custom-rules)	1m 14s
golden (vsphere)	1m 27s
test (release-4.12)	1m 40s
golden (custom-rules)	1m 12s
test (release-4.13)	1m 10s
golden (release-4.12)	1m 14s
test (team-routing)	1m 12s
golden (release-4.13)	1m 15s
golden (team-routing)	1m 23s
	26m 12s

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