feat: isolate populate_obj in a separate method so that it can be easily overriden

[eqperes]

Description

Similar to update_model on Flask-Admin, isolating the call to form.update_obj to a separate method allows the step to be easily overridden. Currently, the methods exposed can access either the form (process_form, for example) or the item (pre_add, pre_update, for example), but not both. Depending on the behavior to be implemented, access to both can be really useful.

ADDITIONAL INFORMATION

• Has associated issue:
• Is CRUD MVC related.
• Is Auth, RBAC security related.
• Changes the security db schema.
• Introduces new feature
• Removes existing feature

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.65%. Comparing base (c65e067) to head (e8140f7).
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2260      +/-   ##
==========================================
+ Coverage   73.81%   74.65%   +0.84%     
==========================================
  Files          72       72              
  Lines        8754     9041     +287     
==========================================
+ Hits         6462     6750     +288     
+ Misses       2292     2291       -1     

Flag	Coverage Δ
python	74.65% <100.00%> (+0.84%)	⬆️

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