📊 war: add 'no relationship' indicator and regional values

[lucasrodes]

Central issue: https://github.com/owid/owid-issues/issues/1221

• Add values at regional level:
  • So far, we only included "number of country-pairs with X relationship" at world level. Now we also include these for each region (regions as defined by COW, I've clarified this in the metadata).
  • A two-country relationship within a region A, is that of two countries both within region A.
• Add 'no relationship' indicator:
  • Besides the 5 different two-country relationship types defined in this dataset, it can also be the case that two countries do not have a relationship at all.