Functor to access to the LHC fill number

For Run 3 it is needed a functor that allows to access to the LHC fill number directly from the online lhcb-conddb information in https://gitlab.cern.ch/lhcb-conddb/lhcb-conditions-database/-/blob/master/Conditions/LHCb/Online/LHC.yml/

Following some suggestions, a possible idea to implement the functionality is to:

• get the condition information in Detector, using a struct similar to the InteractionRegion (named LHCInfo?) developed in Detector!383 (merged) to get the FillNumber reported in each condition file (and all the other information)
• it is needed to add one location to DeLHCb (Conditions/LHCb/Online/LHC.yml) to inform it where to find conditions
• Add tests in Detector to check that the LHC conditions are correctly ported
• Create a struct in Rec that gets the information from Detector (and handles the case when there is no conditions(?)) as done in LHCb!4173 (merged)
• The most straightforward way is to derive all the conditions in a nullary (do not need an input) DELHCB functor and create a series of functors via composition to access them.
• Functors tests are not possible directly in Rec atm because Gaudi services would be required -> Add a test somewhere else to check functor retrieves correctly LHC conditions, like in Moore or DaVinci

(thanks to @raaij for providing the above starting instructions. cc @mfontana @cmarinbe)

cc: @mvesteri, @poluekt