fix(confgen): take subdirs into consideration when build workbook index

[codecov[bot]]

Codecov Report

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

Project coverage is 64.22%. Comparing base (bda9bc5) to head (d1bc96f). Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #140 +/- ## ======================================= Coverage 64.21% 64.22% ======================================= Files 69 69 Lines 7452 7454 +2 ======================================= + Hits 4785 4787 +2 Misses 2105 2105 Partials 562 562 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.