Upgrade docfx to 2.67.3

[mawosoft]

• Add xrefmap-PowerShell.yml Note: docfx has dropped support for xrefservice with >= v2.65.0. Automatic resolve for PowerShell SDK type should theoretically work, but doesn't - hence the additional xrefmap.
• Update convertPlatyPStoDocFxMarkdown.ps1 to filter out unwanted lines from secondary ToCs.

[codecov-commenter]

Codecov Report

Merging #44 (5b0a529) into master (d25b407) will not change coverage. The diff coverage is n/a.

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@@           Coverage Diff           @@
##           master      #44   +/-   ##
=======================================
  Coverage   70.60%   70.60%           
=======================================
  Files          46       46           
  Lines        2058     2058           
  Branches      214      214           
=======================================
  Hits         1453     1453           
  Misses        514      514           
  Partials       91       91