add cleanup observable and use it in generate stories

[silouone]

Detailed purpose of the PR

• Update the generate storybook script and specifly the generated stories to support the removal of stale folder & stories files for stale components ( often the case when having multiple PR to review and switching back and forth to use the storybook

Result and observation

• Breaking changes ?
  If checked, what have you broken ?

• Extra lib ?
  If checked, Which extra lib did you add ? (name, purpose, link ...).

Testing Strategy

• Already covered by tests
• Manual testing
• Unit testing

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.48%. Comparing base (f2d1c6b) to head (5494743).
⚠️ Report is 1100 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2951      +/-   ##
==========================================
- Coverage   95.04%   93.48%   -1.56%     
==========================================
  Files         537      434     -103     
  Lines        8898     6789    -2109     
  Branches      467      472       +5     
==========================================
- Hits         8457     6347    -2110     
  Misses        359      359              
- Partials       82       83       +1     

see 116 files with indirect coverage changes

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