fix: Improvement for the dialog to create a new list, when there is none

[g123k]

Hi everyone!

As noted in #4293, the current dialog shown when there is no user list has some UI issues.
Here is the new look:

[codecov-commenter]

Codecov Report

Merging #4296 (5ff7f31) into develop (cac58a2) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           develop    #4296      +/-   ##
===========================================
- Coverage    10.79%   10.79%   -0.01%     
===========================================
  Files          287      287              
  Lines        14288    14290       +2     
===========================================
  Hits          1542     1542              
- Misses       12746    12748       +2     

Impacted Files	Coverage Δ
...p/lib/generic_lib/dialogs/smooth_alert_dialog.dart	88.18% <ø> (ø)
...app/lib/pages/product_list_user_dialog_helper.dart	0.00% <0.00%> (ø)

... and 2 files with indirect coverage changes

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[g123k]

Thanks for your review @monsieurtanuki