Add validator that checks if any default gift card configuration exists

[loevgaard]

Fixes #211

[codecov]

Codecov Report

Base: 47.13% // Head: 47.13% // No change to project coverage 👍

Coverage data is based on head (2ed81d3) compared to base (2ed81d3).
Patch has no changes to coverable lines.

❗ Current head 2ed81d3 differs from pull request most recent head 589302e. Consider uploading reports for the commit 589302e to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##             0.12.x     #240   +/-   ##
=========================================
  Coverage     47.13%   47.13%           
  Complexity      565      565           
=========================================
  Files           106      106           
  Lines          1765     1765           
=========================================
  Hits            832      832           
  Misses          933      933           

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