Cleanup directories handling

[cmaglie]

Please check if the PR fulfills these requirements

• The PR has no duplicates (please search among the Pull Requests
  before creating one)
• Tests for the changes have been added (for bug fixes / features)

• What kind of change does this PR introduce?
  This PR makes all the directory handling more straightforward.
  All directories computation is now decided in config.go through the getXxxxDirectory() functions.

• What is the current behavior?
  Directory structure and computation were spread across the code.

• What is the new behavior?

• Does this PR introduce a breaking change?

• Other information:

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 124 lines in your changes missing coverage. Please review.
✅ Project coverage is 11.28%. Comparing base (c724474) to head (1d0d5de).
⚠️ Report is 157 commits behind head on main.

Files with missing lines	Patch %	Lines
certificates.go	0.00%	80 Missing ⚠️
config.go	0.00%	22 Missing ⚠️
main.go	0.00%	21 Missing ⚠️
hub.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #765      +/-   ##
==========================================
- Coverage   11.40%   11.28%   -0.12%     
==========================================
  Files          51       51              
  Lines        3910     3951      +41     
==========================================
  Hits          446      446              
- Misses       3409     3450      +41     
  Partials       55       55              

Flag	Coverage Δ
unit	11.28% <0.00%> (-0.12%)	⬇️

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