Add `photolysis_calculator:` configuration

[K20shores]

See #268. Add PhotolysisCalculator struct to mechanism_configuration:: and parsing logic to the v1 parser.

Acceptance criteria

• std::optional<PhotolysisCalculator> photolysis_calculator added to Mechanism
  • likely only needs to provide a filepath
  • we can check that the filepath exists
    • however for tuv, it's configuration file might need to be specified as a relative path, which means the existance check might not be helpful or feasible
  • this would also support cloud j, which we might be adding support for

Ideas

• If we do a path existence check, it belongs in validate(), not `parse()