add xml file of datasets for masterclasses from docdb

Concerning `$n Higgs`, this variable represents "desired file name".  One record can have many files attached, and one file can exist in many formats.  However, we cannot use the same file name for distinct files attached to the same record.  (The file name serves as a sort of unique ID within record context.) E.g. in your record 300 there are files:

- 4lepton.csv
- 4lepton.ig
- 4lepton.json
- diphoton.csv
- diphoton.ig
- diphoton.json

We cannot name them all "Higgs".  There are two possibilities: (1) shall we keep original file names "4lepton", "diphoton"? (2) Or would you like to change file names something else?

In the former case, I can edit your file while merging to amend all the file names.  In the latter case, please edit the file manually in order to enter new distinct desired file names.