Add check for visibility for github_repository

[HorizonNet]

Add a check for the visiblity property of the github_repository
resource from the GitHub provider. It checks if the visibility was not
set to "private". This complies with the latest version of the provider
(3.0.0+), which switches to visibility in favor of the private property.
Left the private property in for backward compatibility.

Resolves #326

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities (and 0 Security Hotspots to review)
0 Code Smells

No Coverage information
No Duplication information

[codecov]

Codecov Report

Merging #333 into master will decrease coverage by 2.19%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #333      +/-   ##
==========================================
- Coverage   63.07%   60.87%   -2.20%     
==========================================
  Files          56       56              
  Lines        1205     1053     -152     
==========================================
- Hits          760      641     -119     
+ Misses        379      346      -33     
  Partials       66       66              

Impacted Files	Coverage Δ
pkg/cli/init.go	20.00% <0.00%> (-8.58%)	⬇️
pkg/cli/server.go	20.00% <0.00%> (-8.58%)	⬇️
pkg/writer/json.go	20.00% <0.00%> (-8.58%)	⬇️
pkg/writer/yaml.go	20.00% <0.00%> (-8.58%)	⬇️
pkg/writer/xml.go	12.50% <0.00%> (-7.50%)	⬇️
pkg/iac-providers/terraform/v12/load-file.go	65.00% <0.00%> (-4.57%)	⬇️
pkg/iac-providers/kubernetes/v1/load-dir.go	83.33% <0.00%> (-3.63%)	⬇️
pkg/policy/opa/engine.go	38.67% <0.00%> (-3.33%)	⬇️
pkg/iac-providers/terraform/v12/convert.go	72.44% <0.00%> (-3.09%)	⬇️
pkg/notifications/webhook/webhook.go	23.52% <0.00%> (-2.79%)	⬇️
... and 45 more

[williepaul]

Nice job!