Alerting: create wrapper for Alertmanager to enable org level isolation (#37320)

Introduces org-level isolation for the Alertmanager and its components.

Silences, Alerts and Contact points are not separated by org and are not shared between them.

Co-authored with @davidmparrott and @papagian

pkg/services/ngalert/notifier/testing.go

@@ -0,0 +1,56 @@
+package notifier
+
+import (
+	"context"
+
+	"github.com/grafana/grafana/pkg/services/ngalert/models"
+	"github.com/grafana/grafana/pkg/services/ngalert/store"
+)
+
+type FakeConfigStore struct {
+	configs map[int64]*models.AlertConfiguration
+}
+
+func (f *FakeConfigStore) GetLatestAlertmanagerConfiguration(query *models.GetLatestAlertmanagerConfigurationQuery) error {
+	var ok bool
+	query.Result, ok = f.configs[query.OrgID]
+	if !ok {
+		return store.ErrNoAlertmanagerConfiguration
+	}
+
+	return nil
+}
+
+func (f *FakeConfigStore) SaveAlertmanagerConfiguration(cmd *models.SaveAlertmanagerConfigurationCmd) error {
+	f.configs[cmd.OrgID] = &models.AlertConfiguration{
+		AlertmanagerConfiguration: cmd.AlertmanagerConfiguration,
+		OrgID:                     cmd.OrgID,
+		ConfigurationVersion:      "v1",
+		Default:                   cmd.Default,
+	}
+
+	return nil
+}
+
+func (f *FakeConfigStore) SaveAlertmanagerConfigurationWithCallback(cmd *models.SaveAlertmanagerConfigurationCmd, callback store.SaveCallback) error {
+	f.configs[cmd.OrgID] = &models.AlertConfiguration{
+		AlertmanagerConfiguration: cmd.AlertmanagerConfiguration,
+		OrgID:                     cmd.OrgID,
+		ConfigurationVersion:      "v1",
+		Default:                   cmd.Default,
+	}
+
+	if err := callback(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+type FakeOrgStore struct {
+	orgs []int64
+}
+
+func (f *FakeOrgStore) GetOrgs(_ context.Context) ([]int64, error) {
+	return f.orgs, nil
+}