Ability to replace primaryKey field via config

[asgraf]

Example use case:

$this->Crud->action()->setConfig('primaryKey', 'uuid');

this change makes FriendsOfCake/crud plugin compatible with dereuromark/cakephp-expose

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (f437194) 90.45% compared to head (90dfe38) 90.46%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #706   +/-   ##
=========================================
  Coverage     90.45%   90.46%           
  Complexity      369      369           
=========================================
  Files            36       36           
  Lines          1153     1154    +1     
=========================================
+ Hits           1043     1044    +1     
  Misses          110      110           

Files	Coverage Δ
src/Traits/FindMethodTrait.php	80.55% <100.00%> (+0.55%)	⬆️

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[ADmad]

• Test(s) required for the change.
• The primaryKey config should be added to $_defaultConfig of all actions that use the FindMethodTrait::_findRecord() method.
• Docs need to be updated to provide info about this new option.