all services: use ConfigItem instead of deprecated ConfigurationItem

The class `ConfigurationItem` from AstroPy is deprecated and will be removed in version 1.0
Can you confirm that this works, i.e. that `VIZIER_TIMEOUT() == conf.timeout` and not `VIZIER_TIMEOUT() == conf.timeout()`?  It is somewhat important that the keyword arguments, e.g. `timeout`, are set to a *value* and not a *reference* - we don't want global configurations to modify *existing* objects, only new instances