Access to InteractionRegion information from DeLHCb

Implement access to information on interaction region position and spread in DeLHCb, as per #47 (closed)

• Skeleton of InteractionRegion struct
• Access to a std:optional of such a struct from DeLHCb
• Allow construction of struct from JSON
  • Update once final format of condition data is known
• Tell DeLHCb where to find the condition
  • Update once final location and name is confirmed
• Handle case where condition is empty - std::optional does not contain a value
• Create test, including test condition data