update Earth discipline structure

[tomkralidis]

• fixes add experimental level #66
• fixes Organize level 8+ sub-topics  #38
• fixes provide publication artifacts #34

Notes:

• reorganized levels can be reviewed in context at https://github.com/wmo-im/wis2-topic-hierarchy/tree/test-structure/topic-hierarchy (this PR branch)
• core levels are relational, and stay as 1 CSV per level
• Earth discipline levels are hierarchical and organized in a directory tree. Sublevels are put forth as directories. Leaf levels are put forth as index.csv files
• CI updated as follows:
  • on each commit to main branch generates https://wmo-im.github.io/wis2-topic-hierarchy/wth-bundle.zip which are all core level CSVs and a bundled CSV of the Earth system discipline. The zipfile is organized in this manner given the abovementioned

[antje-s]

solution variant looks ok to me, even if I have seen a change in the standardisation of values from the solution variant with common topic-level value files over all domains

[tomkralidis]

TT-WISMD 2023-11-17:

• removed earth-system-discipline-subcategory from topic-hierarchy.csv
• add text to specification
  • domains SHALL use a hierarchy only (not relational)
  • experimental SHOULD NOT be a permanent solution

[tomkralidis]

@wmo-im/tt-wismd FYI this PR has now been updated per the discussion in #70 (comment). Please review and provide feedback or approve.