ShortenedThrowableConverter: add option to set my own custom abbreviator

[brenuart]

No description provided.

[codecov]

Codecov Report

Merging #893 (a1c21ef) into main (e1c6129) will decrease coverage by 0.22%.
The diff coverage is 67.90%.

@@             Coverage Diff              @@
##               main     #893      +/-   ##
============================================
- Coverage     71.79%   71.56%   -0.23%     
- Complexity     1334     1347      +13     
============================================
  Files           170      173       +3     
  Lines          4939     4984      +45     
  Branches        520      518       -2     
============================================
+ Hits           3546     3567      +21     
- Misses         1149     1164      +15     
- Partials        244      253       +9     

Impacted Files	Coverage Δ
.../java/net/logstash/logback/CachingAbbreviator.java	0.00% <0.00%> (-100.00%)	⬇️
...ain/java/net/logstash/logback/NullAbbreviator.java	0.00% <0.00%> (-100.00%)	⬇️
...composite/loggingevent/LoggerNameJsonProvider.java	61.53% <28.57%> (-34.30%)	⬇️
...ogback/stacktrace/ShortenedThrowableConverter.java	79.03% <50.00%> (-1.87%)	⬇️
...n/java/net/logstash/logback/util/LogbackUtils.java	64.70% <75.00%> (+24.70%)	⬆️
...ck/abbreviator/DefaultTargetLengthAbbreviator.java	92.00% <92.00%> (ø)
...gstash/logback/abbreviator/CachingAbbreviator.java	100.00% <100.00%> (ø)
.../logstash/logback/abbreviator/NullAbbreviator.java	100.00% <100.00%> (ø)
...h/logback/composite/FastISOTimestampFormatter.java	94.89% <0.00%> (-1.03%)	⬇️

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