Docker: Move files to the top directory.

[hmdne]

This removes symlinks which are particularly troublesome on Win32 systems. This fixes #104

Metanorma PR checklist

• Breaking changes (list related PRs)
• Documentation update required (create task for this)
• External dependency introduced (documentation update need)
• Gem with native library introduced

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.34%. Comparing base (defb04a) to head (5246248).
Report is 81 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #105      +/-   ##
==========================================
+ Coverage   96.67%   98.34%   +1.66%     
==========================================
  Files          42       46       +4     
  Lines        1054     1327     +273     
==========================================
+ Hits         1019     1305     +286     
+ Misses         35       22      -13     

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