feat: add kafka-preferred-replica-election command (closes #3)

[devshawn]

Description

Adds support for kafka-preferred-replica-election and allows auto filling admin.client for it.

[codecov-io]

Codecov Report

Merging #10 into master will increase coverage by 0.04%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #10      +/-   ##
==========================================
+ Coverage    96.7%   96.75%   +0.04%     
==========================================
  Files          12       12              
  Lines         546      554       +8     
==========================================
+ Hits          528      536       +8     
  Misses         18       18

Impacted Files	Coverage Δ
kafkashell/executor.py	100% <100%> (ø)	⬆️
kafkashell/constants.py	100% <100%> (ø)	⬆️

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