Use yml arrays to list the ForbiddenImports

[BraisGabin]

Fixes #2463

I think that we should add this to the rest of configurations that have lists and deprecate the strings splitted by ,. And remove the support in 2.0. My reasons:

• It's easier to mantain the configuration using lists than strings
• We don't need to handle strange cases splitting strings (empty strings and similar)

If you agree I can open an issue to track all those configurations.

[codecov-io]

Codecov Report

Merging #2474 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##             master   #2474      +/-   ##
===========================================
+ Coverage     83.29%   83.3%   +0.01%     
  Complexity     2196    2196              
===========================================
  Files           360     360              
  Lines          6225    6230       +5     
  Branches       1144    1144              
===========================================
+ Hits           5185    5190       +5     
  Misses          463     463              
  Partials        577     577

Impacted Files	Coverage Δ	Complexity Δ
...n/kotlin/io/gitlab/arturbosch/detekt/rules/Junk.kt	68.75% <100%> (+18.75%)	0 <0> (ø)	⬇️
...b/arturbosch/detekt/rules/style/ForbiddenImport.kt	94.73% <100%> (-0.27%)	9 <0> (ø)
...turbosch/detekt/rules/style/ForbiddenMethodCall.kt	86.66% <100%> (ø)	5 <0> (ø)	⬇️

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