Replace signed in user for identity.requester (#73750)

* Make identity.Requester available at Context

* Clean pkg/services/guardian/guardian.go

* Clean guardian provider and guardian AC

* Clean pkg/api/team.go

* Clean ctxhandler, datasources, plugin and live

* Question: what to do with the UserDisplayDTO?

* Clean dashboards and guardian

* Remove identity.Requester from ReqContext

* Implement NewUserDisplayDTOFromRequester

* Fix tests

* Change status code numbers for http constants

* Upgrade signature of ngalert services

* log parsing errors instead of throwing error

* Fix tests and add logs

* linting

pkg/services/alerting/models.go

@@ -4,8 +4,8 @@ import (
 	"sync"
 
 	"github.com/grafana/grafana/pkg/components/null"
+	"github.com/grafana/grafana/pkg/services/auth/identity"
 	"github.com/grafana/grafana/pkg/services/dashboards"
-	"github.com/grafana/grafana/pkg/services/user"
 )
 
 // Job holds state about when the alert rule should be evaluated.
@@ -46,7 +46,7 @@ type EvalMatch struct {
 }
 
 type DashAlertInfo struct {
-	User  *user.SignedInUser
+	User  identity.Requester
 	Dash  *dashboards.Dashboard
 	OrgID int64
 }