ISO 19115: put details into field <supplementalInformation>

[AlexDo1]

With this PR, details are no longer stored in the ISO field <abstract> but in <supplementalInformation> instead.

Closes #266

[codecov[bot]]

Codecov Report

Merging #289 (8694227) into main (2143310) will decrease coverage by 0.03%. The diff coverage is 68.75%.

@@            Coverage Diff             @@
##             main     #289      +/-   ##
==========================================
- Coverage   64.06%   64.04%   -0.03%     
==========================================
  Files          75       75              
  Lines        3838     3830       -8     
==========================================
- Hits         2459     2453       -6     
+ Misses       1379     1377       -2     

Flag	Coverage Δ
e2e	64.04% <68.75%> (-0.03%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
metacatalog/ext/standards_export/util.py	80.76% <66.66%> (+0.76%)	:arrow_up:
metacatalog/ext/standards_export/extension.py	94.52% <71.42%> (-2.59%)	:arrow_down:

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[AlexDo1]

@mmaelicke can you add your review?