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/user/identity.go

@@ -43,6 +43,9 @@ func (u *SignedInUser) NameOrFallback() string {
 	return u.Email
 }
 
+// TODO: There's a need to remove this struct since it creates a circular dependency
+
+// DEPRECATED: This function uses `UserDisplayDTO` model which we want to remove
 func (u *SignedInUser) ToUserDisplayDTO() *UserDisplayDTO {
 	return &UserDisplayDTO{
 		ID:    u.UserID,
@@ -51,6 +54,16 @@ func (u *SignedInUser) ToUserDisplayDTO() *UserDisplayDTO {
 	}
 }
 
+// Static function to parse a requester into a UserDisplayDTO
+func NewUserDisplayDTOFromRequester(requester identity.Requester) (*UserDisplayDTO, error) {
+	userID, _ := identity.IntIdentifier(requester.GetNamespacedID())
+	return &UserDisplayDTO{
+		ID:    userID,
+		Login: requester.GetLogin(),
+		Name:  requester.GetDisplayName(),
+	}, nil
+}
+
 func (u *SignedInUser) HasRole(role roletype.RoleType) bool {
 	if u.IsGrafanaAdmin {
 		return true