Alerting: Condition evaluator with cached pipeline (#57479)

* create rule evaluator
* load header from the context
* init one factory
* update scheduler

pkg/services/ngalert/eval/eval_mocks/FakeFactory.go

@@ -0,0 +1,32 @@
+package eval_mocks
+
+import (
+	"errors"
+
+	"github.com/grafana/grafana/pkg/services/ngalert/eval"
+	"github.com/grafana/grafana/pkg/services/ngalert/models"
+)
+
+type fakeEvaluatorFactory struct {
+	err       error
+	evaluator eval.ConditionEvaluator
+}
+
+func NewEvaluatorFactory(evaluator eval.ConditionEvaluator) eval.EvaluatorFactory {
+	return &fakeEvaluatorFactory{evaluator: evaluator}
+}
+
+func NewFailingEvaluatorFactory(err error) eval.EvaluatorFactory {
+	if err == nil {
+		err = errors.New("test")
+	}
+	return &fakeEvaluatorFactory{err: err}
+}
+
+func (f fakeEvaluatorFactory) Validate(ctx eval.EvaluationContext, condition models.Condition) error {
+	return f.err
+}
+
+func (f fakeEvaluatorFactory) Create(ctx eval.EvaluationContext, condition models.Condition) (eval.ConditionEvaluator, error) {
+	return f.evaluator, f.err
+}