[docs] Disable progress bar for jupyter notebook convertion

[frankfliu]

Description

Brief description of what this PR is about

• If this change is a backward incompatible change, why must this change be made?
• Interesting edge cases to note here

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 50.00000% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 72.30%. Comparing base (93123ad) to head (15d2071).
Report is 1 commits behind head on master.

Files	Patch %	Lines
...rc/main/java/ai/djl/training/util/ProgressBar.java	50.00%	0 Missing and 3 partials ⚠️

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Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3017      +/-   ##
============================================
- Coverage     72.31%   72.30%   -0.01%     
- Complexity     7290     7292       +2     
============================================
  Files           722      722              
  Lines         32496    32499       +3     
  Branches       3390     3392       +2     
============================================
+ Hits          23498    23499       +1     
  Misses         7380     7380              
- Partials       1618     1620       +2     

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