Display dynamic --jvm-target values when using --help flag

[3flex]

This will now print values supported by the embedded Kotlin version and won't have to be updated manually anymore.

The required toString override was introduced in Kotlin 1.6.20 thanks to my first PR on jetbrains/kotlin :)

Before:

    --jvm-target
      EXPERIMENTAL: Target version of the generated JVM bytecode that was 
      generated during compilation and is now being used for type resolution 
      (1.6, 1.8, 9, 10, 11, 12, 13, 14, 15, 16 or 17)
      Default: 1.8

After:

    --jvm-target
      EXPERIMENTAL: Target version of the generated JVM bytecode that was 
      generated during compilation and is now being used for type resolution
      Default: 1.8
      Possible Values: [1.6, 1.8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18]

[codecov]

Codecov Report

Merging #4694 (7f86eb9) into main (ed8b089) will decrease coverage by 0.01%.
The diff coverage is 50.00%.

@@             Coverage Diff              @@
##               main    #4694      +/-   ##
============================================
- Coverage     84.45%   84.44%   -0.02%     
  Complexity     3436     3436              
============================================
  Files           492      492              
  Lines         11335    11337       +2     
  Branches       2082     2083       +1     
============================================
  Hits           9573     9573              
- Misses          701      703       +2     
  Partials       1061     1061              

Impacted Files	Coverage Δ
...gitlab/arturbosch/detekt/cli/ArgumentConverters.kt	69.23% <0.00%> (-5.77%)	⬇️
.../kotlin/io/gitlab/arturbosch/detekt/cli/CliArgs.kt	100.00% <100.00%> (ø)
...ain/kotlin/io/gitlab/arturbosch/detekt/cli/Spec.kt	88.70% <100.00%> (ø)

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