Access control: Rename predefined roles to fixed roles (code) (#34469) (#34663)

* s/grafana:roles:/fixed:/

* Update free text references to predefined roles

(cherry picked from commit 0f4806db8a)

Co-authored-by: Emil Tullstedt <emil.tullstedt@grafana.com>

pkg/services/accesscontrol/ossaccesscontrol/ossaccesscontrol.go

@@ -62,9 +62,9 @@ func (ac *OSSAccessControlService) GetUserPermissions(ctx context.Context, user
 	builtinRoles := ac.GetUserBuiltInRoles(user)
 	permissions := make([]*accesscontrol.Permission, 0)
 	for _, builtin := range builtinRoles {
-		if roleNames, ok := accesscontrol.PredefinedRoleGrants[builtin]; ok {
+		if roleNames, ok := accesscontrol.FixedRoleGrants[builtin]; ok {
 			for _, name := range roleNames {
-				r, exists := accesscontrol.PredefinedRoles[name]
+				r, exists := accesscontrol.FixedRoles[name]
 				if !exists {
 					continue
 				}