Alerting: Condition evaluator with cached pipeline (#57479)

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

pkg/services/ngalert/eval/context.go

@@ -2,42 +2,19 @@ package eval
 
 import (
 	"context"
-	"time"
 
-	"github.com/grafana/grafana/pkg/services/ngalert/models"
 	"github.com/grafana/grafana/pkg/services/user"
 )
 
 // EvaluationContext represents the context in which a condition is evaluated.
 type EvaluationContext struct {
-	Ctx     context.Context
-	User    *user.SignedInUser
-	At      time.Time
-	RuleUID string
+	Ctx  context.Context
+	User *user.SignedInUser
 }
 
 func Context(ctx context.Context, user *user.SignedInUser) EvaluationContext {
 	return EvaluationContext{
 		Ctx:  ctx,
 		User: user,
-		At:   time.Now(),
 	}
 }
-
-func (c EvaluationContext) When(t time.Time) EvaluationContext {
-	c.At = t
-	return c
-}
-
-func (c EvaluationContext) WithRule(r *models.AlertRule) EvaluationContext {
-	if r != nil {
-		c.RuleUID = r.UID
-	}
-	return c
-}
-
-func (c EvaluationContext) WithTimeout(timeout time.Duration) (EvaluationContext, context.CancelFunc) {
-	timeoutCtx, cancel := context.WithTimeout(c.Ctx, timeout)
-	c.Ctx = timeoutCtx
-	return c, cancel
-}