Fix refresh token max length (occurs with Microsoft OAuth)

[richardARPANET]

Fix for:

value too long for type character varying(255)

refresh_token = get_refresh_token_model().objects.create(
        user=org_user,
        token=token_data['refresh_token'],
        application=application,
        access_token=access_token,
        token_family=token_family,
    )

255 is far too short, as per OAuth guidelines. changed to 8000. Now Microsoft OAuth works.