Docs: importing any netcdf/xarray into qcodes database

[astafan8]

main purpose is to use this to load netcdf/xarray data into qcodes database for use cases where other tools actually need the raw data in the database.

very initial working example.

[codecov[bot]]

Codecov Report

Merging #3635 (c9f08a2) into master (70fb10d) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3635   +/-   ##
=======================================
  Coverage   65.74%   65.74%           
=======================================
  Files         225      225           
  Lines       30520    30520           
=======================================
  Hits        20064    20064           
  Misses      10456    10456