Alerting: Refactor store to not export its own interface for InstanceStore, delete dead dependency injection (#55772)

* Add consumer-side store interface to state manager

* Remove dead dependency

* Delete dead dependency in API struct

* Delete store-layer InstanceStore interface

* Move fake for state's InstanceStore interface to state package

pkg/services/ngalert/state/testing.go

@@ -0,0 +1,37 @@
+package state
+
+import (
+	"context"
+	"sync"
+
+	"github.com/grafana/grafana/pkg/services/ngalert/models"
+)
+
+type FakeInstanceStore struct {
+	mtx         sync.Mutex
+	RecordedOps []interface{}
+}
+
+func (f *FakeInstanceStore) ListAlertInstances(_ context.Context, q *models.ListAlertInstancesQuery) error {
+	f.mtx.Lock()
+	defer f.mtx.Unlock()
+	f.RecordedOps = append(f.RecordedOps, *q)
+	return nil
+}
+
+func (f *FakeInstanceStore) SaveAlertInstance(_ context.Context, q *models.SaveAlertInstanceCommand) error {
+	f.mtx.Lock()
+	defer f.mtx.Unlock()
+	f.RecordedOps = append(f.RecordedOps, *q)
+	return nil
+}
+
+func (f *FakeInstanceStore) FetchOrgIds(_ context.Context) ([]int64, error) { return []int64{}, nil }
+
+func (f *FakeInstanceStore) DeleteAlertInstance(_ context.Context, _ int64, _, _ string) error {
+	return nil
+}
+
+func (f *FakeInstanceStore) DeleteAlertInstancesByRule(ctx context.Context, key models.AlertRuleKey) error {
+	return nil
+}