Expand run-as-non-root template to verify runAsGroup field is nonzero.

[ariyonaty]

Closes #748

This PR introduces changes which expand the run-as-non-root template/check to verify runAsGroup field is set to a non-zero value.

The runAsGroup field specifies the group ID under which the container’s process should run.
If left unspecified, the GID defaults to 0.

Snippet of build in action where pod.yaml for first execution initially didn't set runAsGroup, second execution set the field to 0, and finally set to a non-zero value:

[codecov]

Codecov Report

Attention: Patch coverage is 52.38095% with 10 lines in your changes missing coverage. Please review.

Project coverage is 62.34%. Comparing base (dbd7529) to head (6331670).
Report is 29 commits behind head on main.

Files	Patch %	Lines
pkg/templates/runasnonroot/template.go	52.38%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #804      +/-   ##
==========================================
- Coverage   62.36%   62.34%   -0.02%     
==========================================
  Files         197      197              
  Lines        4854     4871      +17     
==========================================
+ Hits         3027     3037      +10     
- Misses       1439     1447       +8     
+ Partials      388      387       -1     

Flag	Coverage Δ
unit	62.34% <52.38%> (-0.02%)	⬇️

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[janisz]

could you add unit tests for new code?

[janisz]

How about extracting a function to check for non zero int pointer?

func isNonZero(number *int64) bool {
	return number != nil && *number > 0
}