Auth: Add empty role definition (#64694)

* Allow setting role as None

Co-authored-by: gamab <gabi.mabs@gmail.com>

Seeking for places where role.None would be used

Co-authored-by: Jguer <joao.guerreiro@grafana.com>

Adding None role to the frontend

Co-authored-by: Jguer <joao.guerreiro@grafana.com>

unify org role declaration and remove from add permission

fix backend test

fix backend lint

* remove role none from frontend

* Simplify checks

Co-authored-by: Kalle Persson <kalle.persson@grafana.com>

* nits

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Co-authored-by: Kalle Persson <kalle.persson@grafana.com>

pkg/services/accesscontrol/errors.go

@@ -8,6 +8,7 @@ import (
 var (
 	ErrFixedRolePrefixMissing = errors.New("fixed role should be prefixed with '" + FixedRolePrefix + "'")
 	ErrInvalidBuiltinRole     = errors.New("built-in role is not valid")
+	ErrNoneRoleAssignment     = errors.New("none role cannot receive permissions")
 	ErrInvalidScope           = errors.New("invalid scope")
 	ErrResolverNotFound       = errors.New("no resolver found")
 	ErrPluginIDRequired       = errors.New("plugin ID is required")