Alerting: Create abstraction for launching transactions and refactor existing transaction management to use it (#46216)

* Remove InTransaction from RuleStore and make it its own interface

* Ensure that ctx-based is clear from name

* Resolve merge conflicts

* Refactor tests to work in terms of the introduced abstraction rather than concrete dbstore

pkg/services/ngalert/api/api_ruler.go

@@ -27,6 +27,7 @@ import (
 )
 
 type RulerSrv struct {
+	xactManager     store.TransactionManager
 	store           store.RuleStore
 	DatasourceCache datasources.CacheService
 	QuotaService    *quota.QuotaService
@@ -263,7 +264,7 @@ func (srv RulerSrv) updateAlertRulesInGroup(c *models.ReqContext, namespace *mod
 	// TODO add create rules authz logic
 
 	var groupChanges *changes = nil
-	err := srv.store.InTransaction(c.Req.Context(), func(tranCtx context.Context) error {
+	err := srv.xactManager.InTransaction(c.Req.Context(), func(tranCtx context.Context) error {
 		var err error
 		groupChanges, err = calculateChanges(tranCtx, srv.store, c.SignedInUser.OrgId, namespace, groupName, rules)
 		if err != nil {