[refactor!] Use `MapNullableParameter` enum to improve readability

**Describe the solution you'd like**
```csharp
// maps following routes
// apps/-/instances/-/roles
// apps/{appName}/instances/-/roles
// apps/-/instances/{instanceId}/roles
// apps/{appName}/instances/{instanceId}/roles
v1.MapQuery<ListInstanceRolesQuery>("apps/{appName}/instances/{instanceId}/roles", MapNullableParameter.Enable);
```