[BUG] Service token is required to create RemoteAuthDataLoaderImpl

[shurwit]

Describe the bug
The NewRemoteAuthDataLoader() function currently requires the implementing service to provide a service token to return a successfully. This should not be necessary unless functionality that requires a service token is enabled (eg. DeletedAccountsCallback).

To Reproduce
Steps to reproduce the behavior:

1. Call NewRemoteAuthDataLoader() with configs only including the AuthServiceHost
2. Receive error indicating that the service token is missing: error constructing data loader config: service token is missing

Expected behavior
The NewRemoteAuthDataLoader() function should return successfully even if the ServiceToken config is not provided and features requiring authorization are not configured.