Implement zsh completion generator

[dominikschulz]

Fixes #557

[codecov]

Codecov Report

Merging #565 into master will increase coverage by 0.2%.
The diff coverage is 36.66%.

@@            Coverage Diff            @@
##           master     #565     +/-   ##
=========================================
+ Coverage   21.52%   21.73%   +0.2%     
=========================================
  Files         108      110      +2     
  Lines        6393     6507    +114     
=========================================
+ Hits         1376     1414     +38     
- Misses       4742     4807     +65     
- Partials      275      286     +11

Impacted Files	Coverage Δ
main.go	5.9% <0%> (-0.12%)	⬇️
utils/completion/zsh/completion.go	27.27% <27.27%> (ø)
utils/completion/fish/completion.go	42.37% <42.37%> (ø)
action/completion.go	83.33% <63.63%> (-10.22%)	⬇️

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