Assignment operator increases indent with extened option

[petertrr]

What's done:

• Updated logic
• Added tests

This pull request closes #239

[codecov]

Codecov Report

Merging #338 into master will decrease coverage by 0.05%.
The diff coverage is 60.00%.

@@             Coverage Diff              @@
##             master     #338      +/-   ##
============================================
- Coverage     82.88%   82.82%   -0.06%     
- Complexity     1125     1127       +2     
============================================
  Files            54       54              
  Lines          2798     2800       +2     
  Branches        890      893       +3     
============================================
  Hits           2319     2319              
  Misses          162      162              
- Partials        317      319       +2     

Flag	Coverage Δ	Complexity Δ
#unittests	82.82% <60.00%> (-0.06%)	1127.00 <0.00> (+2.00)	⬇️

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Impacted Files	Coverage Δ	Complexity Δ
.../cqfn/diktat/ruleset/utils/indentation/Checkers.kt	71.42% <0.00%> (-1.43%)	0.00 <0.00> (ø)
...cqfn/diktat/ruleset/rules/files/IndentationRule.kt	89.61% <75.00%> (+0.27%)	23.00 <0.00> (+3.00)
...tat/ruleset/utils/indentation/IndentationConfig.kt	50.00% <0.00%> (-16.67%)	8.00% <0.00%> (-1.00%)

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[orchestr7]

lgtm