Alerting: Add traceability headers for alert queries (#57127)

* Define EvaluationContext

* Refactor ConditionEval to use new context struct

* Refactor QueriesAndExpressionsEval to use EvaluationContext

* Remove dead field from AlertExecCtx

* Refactor Validate to use EvaluationContext

* Get rid of privately used AlertExecCtx

* Move EvaluationContext to new file and add helper

* Add builder pattern and bind rule info to context

* Extract header logic and add rule UID header

* Fix missing call

pkg/services/ngalert/eval/eval_test.go

@@ -445,8 +445,9 @@ func TestValidate(t *testing.T) {
 			condition := testCase.condition(cacheService)
 
 			evaluator := NewEvaluator(&setting.Cfg{ExpressionsEnabled: true}, log.New("test"), cacheService, expr.ProvideService(&setting.Cfg{ExpressionsEnabled: true}, nil, nil))
+			evalCtx := Context(context.Background(), u)
 
-			err := evaluator.Validate(context.Background(), u, condition)
+			err := evaluator.Validate(evalCtx, condition)
 			if testCase.error {
 				require.Error(t, err)
 			} else {