fix: add items field label

[s-aga-r]

Source / Ref: ISS-23-24-00171

Problem: Since the Label was removed in #32408, when the user tries to download the template (Data Import) the label comes as None.

Changes: Add items field Label in Purchase Order, Supplier Quotation and Quotation.

Before:

After:

[codecov]

Codecov Report

Merging #34860 (a78b4be) into develop (e4f152a) will decrease coverage by 0.01%.
The diff coverage is n/a.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #34860      +/-   ##
===========================================
- Coverage    63.86%   63.86%   -0.01%     
===========================================
  Files          810      810              
  Lines        59745    59745              
===========================================
- Hits         38159    38158       -1     
- Misses       21586    21587       +1     

see 2 files with indirect coverage changes