Deprecate implementations of Config

[arturbosch]

Rule authors do not need to know about internal implementations of YamlConfig etc.
They know that the yaml format config is supported and what methods can be used with a Config object.

#2365

[codecov-io]

Codecov Report

Merging #2420 into master will decrease coverage by 0.01%.
The diff coverage is 80.3%.

@@             Coverage Diff              @@
##             master    #2420      +/-   ##
============================================
- Coverage     82.87%   82.85%   -0.02%     
- Complexity     2157     2174      +17     
============================================
  Files           354      356       +2     
  Lines          6136     6137       +1     
  Branches       1122     1121       -1     
============================================
  Hits           5085     5085              
- Misses          475      476       +1     
  Partials        576      576

Impacted Files	Coverage Δ	Complexity Δ
...ch/detekt/api/internal/ValidatableConfiguration.kt	100% <ø> (ø)	0 <0> (ø)	⬇️
.../io/gitlab/arturbosch/detekt/cli/Configurations.kt	78.78% <ø> (ø)	0 <0> (ø)	⬇️
...n/kotlin/io/gitlab/arturbosch/detekt/api/Config.kt	93.75% <ø> (+3.75%)	0 <0> (ø)	⬇️
.../arturbosch/detekt/api/internal/CompositeConfig.kt	66.66% <66.66%> (ø)	5 <5> (?)
...itlab/arturbosch/detekt/api/internal/YamlConfig.kt	76.92% <76.92%> (ø)	8 <8> (?)
...tlab/arturbosch/detekt/api/internal/EmptyConfig.kt	83.33% <83.33%> (ø)	5 <5> (?)
...itlab/arturbosch/detekt/api/internal/BaseConfig.kt	85.71% <85.71%> (ø)	12 <12> (?)
... and 1 more

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