[improve] Install coreutils in docker image to improve compatibility

[lhotari]

Resolves apache/pulsar-helm-chart#554

Motivation

• the timeout command provided by default busybox implementation in Alpine leaves zombie processes
  • see [timeout] <defunct> Zookeeper and Broker Pods Contain Zombie Processes pulsar-helm-chart#554 for details

Modifications

• add coreutils package to the docker image. The size of coreutils is small, only about 1MB.

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.39%. Comparing base (bbc6224) to head (5b5c3c0).
Report is 771 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #23667      +/-   ##
============================================
+ Coverage     73.57%   74.39%   +0.82%     
- Complexity    32624    34520    +1896     
============================================
  Files          1877     1944      +67     
  Lines        139502   147331    +7829     
  Branches      15299    16258     +959     
============================================
+ Hits         102638   109614    +6976     
- Misses        28908    29263     +355     
- Partials       7956     8454     +498     

Flag	Coverage Δ
inttests	27.27% <ø> (+2.69%)	⬆️
systests	24.37% <ø> (+0.05%)	⬆️
unittests	73.77% <ø> (+0.92%)	⬆️

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see 665 files with indirect coverage changes