Help returns exit 0 code

[pahatz]

Related issue(s) and PR(s)
This PR closes #313

Description
Currently sda-cli does not return the correct exit code when we run help or -h (exit 1)
It should return exit code 0 except the case of asking for a wrong subcommand.

How to test
Run:

./sda-cli help
./sda-cli -h
./sda-cli help list
./sda-cli help inexistent_command

followed each time by:

echo $?

to get the exit code of the previous command.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 40.48%. Comparing base (19233e3) to head (db980ed).
Report is 6 commits behind head on main.

Files	Patch %	Lines
main.go	0.00%	9 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #389      +/-   ##
==========================================
- Coverage   40.55%   40.48%   -0.08%     
==========================================
  Files          11       11              
  Lines        1536     1539       +3     
==========================================
  Hits          623      623              
- Misses        834      837       +3     
  Partials       79       79              

Flag	Coverage Δ
unittests	40.48% <0.00%> (-0.08%)	⬇️

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[MalinAhlberg]

Well done, and thanks for the nice instructions! I think there is one more case where exit 1 should be returned, made a comment. Apart from that, I'm ready to approve.