Add semantics checks for nightly slots configurations
at the moment we only check that the slot configurations can be loaded, but that only accounts for some basic errors, and not that the configuration is valid (see LHCbNightlyConf!304 (merged)).
at the moment we only check that the slot configurations can be loaded, but that only accounts for some basic errors, and not that the configuration is valid (see LHCbNightlyConf!304 (merged)).