feat: #2248 - user agent distinction between scan and barcode search

[monsieurtanuki]

Impacted files:

• barcode_product_query.dart: new parameter isScanned to distinguish scan and barcode search via the user agent comment field
• continuous_scan_model.dart: "this IS a scan"
• product_dialog_helper.dart: "this is NOT a scan"
• product_query.dart: new method to set the user agent comment field

What

• Barcode scan and barcode search use the same search URL.
• We were asked to distinguish them via the user agent.
• The user agent comment will be different, and will be either 'scan' or 'search'.

Fixes bug(s)

• Closes: Sending a more explicit header when doing a scan/query from Smoothie #2248

[codecov-commenter]

Codecov Report

Merging #2408 (c3e6f2f) into develop (2ea0da3) will decrease coverage by 1.32%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           develop   #2408      +/-   ##
==========================================
- Coverage     8.86%   7.53%   -1.33%     
==========================================
  Files          161     204      +43     
  Lines         6623    9751    +3128     
==========================================
+ Hits           587     735     +148     
- Misses        6036    9016    +2980     

Impacted Files	Coverage Δ
...kages/smooth_app/lib/widgets/attribute_button.dart	0.00% <0.00%> (-92.00%)	⬇️
...s/smooth_app/lib/data_models/user_preferences.dart	8.73% <0.00%> (-23.57%)	⬇️
packages/smooth_app/lib/themes/smooth_theme.dart	60.00% <0.00%> (-22.98%)	⬇️
...p/lib/generic_lib/dialogs/smooth_alert_dialog.dart	15.29% <0.00%> (-18.92%)	⬇️
...mooth_app/lib/data_models/product_preferences.dart	24.65% <0.00%> (-6.78%)	⬇️
packages/smooth_app/lib/main.dart	14.40% <0.00%> (-3.49%)	⬇️
.../smooth_app/lib/pages/onboarding/welcome_page.dart	0.00% <0.00%> (-3.13%)	⬇️
.../smooth_app/lib/pages/onboarding/scan_example.dart	0.00% <0.00%> (-2.28%)	⬇️
...p/lib/pages/onboarding/consent_analytics_page.dart	0.00% <0.00%> (-1.57%)	⬇️
...smooth_app/lib/pages/product/new_product_page.dart	0.00% <0.00%> (-0.88%)	⬇️
... and 203 more

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