Alerting: validate rules and calculate changes in API controller (#45072)

* Update API controller
   - add validation of rules API model
   - add function to calculate changes between the submitted alerts and existing alerts
   - update RoutePostNameRulesConfig to validate input models, calculate changes and apply in a transaction

* Update DBStore
   - delete unused storage method. All the logic is moved upstream.
   - upsert to not modify fields of new by values from the existing alert
   - if rule has UID do not try to pull it from db. (it is done upstream)

* Add rule generator

pkg/services/ngalert/api/util.go

@@ -202,6 +202,13 @@ func validateCondition(ctx context.Context, c ngmodels.Condition, user *models.S
 	return nil
 }
 
+// conditionValidator returns a curried validateCondition that accepts only condition
+func conditionValidator(c *models.ReqContext, cache datasources.CacheService) func(ngmodels.Condition) error {
+	return func(condition ngmodels.Condition) error {
+		return validateCondition(c.Req.Context(), condition, c.SignedInUser, c.SkipCache, cache)
+	}
+}
+
 func validateQueriesAndExpressions(ctx context.Context, data []ngmodels.AlertQuery, user *models.SignedInUser, skipCache bool, datasourceCache datasources.CacheService) (map[string]struct{}, error) {
 	refIDs := make(map[string]struct{})
 	if len(data) == 0 {