Add machine-readable BKS JSON for FJSPLib, consistent with JSPLib

Hi, thanks for maintaining this excellent benchmark repository.

I noticed that for JSPLib/jobshop the best-known results are available in a structured JSON format, whereas for FJSPLib/flexible jobshop the best-known bounds seem to be recorded only in the README/webpage tables.

Would it be possible to add the same machine-readable BKS format for FJSPLib as is already provided for JSPLib?