* Alerting: Update grafana/alerting
* make tests pass by implementing yaml unmarshallers and deleting fields with omitempty in their yaml tags
* go mod tidy
* fix tests by implementing not calling GettableApiAlertingConfig.UnmarshalYAML from GettableApiAlertingConfig.UnmarshalJSON
* cleanup, reduce diff
* fix more tests
* update grafana/alerting to latest commit, delete global section from configs in tests
* bring back YAML unmarshaller for GettableApiAlertingConfig
* update alerting package dependency to point to main
* skip test for sns notifier
Alexander Akhmetov
Yuri Tseretyan
Santiago