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[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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

Additional details and impacted files

```diff @@ 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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