refactor: Use Var function for flags which don't have shorthand

[johnmanjiro13]

VarP of pflag package receive a shorthand.
However, some flags don't need a shorthand, in which case it's better to use Var function.
https://pkg.go.dev/github.com/spf13/pflag#FlagSet.String

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (7745851) 53.95% compared to head (7dc32ce) 53.95%.
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #104   +/-   ##
=======================================
  Coverage   53.95%   53.95%           
=======================================
  Files           5        5           
  Lines         341      341           
=======================================
  Hits          184      184           
  Misses        139      139           
  Partials       18       18           

Files	Coverage Δ
root.go	90.90% <100.00%> (ø)

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