Example: update HDF5 "import and export" to use operators.result.custom

[oparreno]

• Add result_name pin in custom operator.
• Modify 02-hdf5_serialize_and_read example to use the source operator instead.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.61%. Comparing base (74c4691) to head (d625581).
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2045      +/-   ##
==========================================
- Coverage   88.62%   88.61%   -0.01%     
==========================================
  Files          90       90              
  Lines       10225    10225              
==========================================
- Hits         9062     9061       -1     
- Misses       1163     1164       +1     

[rafacanton]

@oparreno The operators code is autogenerated, we shouldn't modify it manually. Changes will be ported from the server when the hdf5 issue is fixed