add an option to have the default value as a list with commas as seperator

[n3aka]

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The idea was like mentioned on the title to be able to specify multiple default values that will come back as a slice

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.70%. Comparing base (6703dea) to head (2e7b385).
Report is 337 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2744   +/-   ##
=======================================
  Coverage   98.69%   98.70%           
=======================================
  Files          41       41           
  Lines        2074     2079    +5     
=======================================
+ Hits         2047     2052    +5     
  Misses         15       15           
  Partials       12       12           

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[takanuva15]

@appleboy Hi, can we get this PR merged since it was already approved? (I can make a copy of this PR with conflicts fixed if that's the only blocker to getting this released publicly)