Some `shellcheck` fixes and new input to print Hadolint results to console

[ViacheslavKudinov]

• few shellcheck fixes
• added results-to-console input to be able to print results to console
• added integration testing job to test new input and recursive
• used env to avoid script injection during integration testing
• updated documentation

Could be considered as a potential fix of https://github.com/hadolint/hadolint-action/issues/60

Contains script injection fixes from https://github.com/hadolint/hadolint-action/pull/62

[lorenzo]

Thanks for your contribution! would you mind resolving the merge conflicts?

[ViacheslavKudinov]

Sure, I will take a look and update.

[lorenzo]

thanks!

[ViacheslavKudinov]

HI @lorenzo I see that this PR https://github.com/hadolint/hadolint-action/pull/71 changed behavior and input which I've added a kind of duplication to get output and useless. But if you can revert my PR merged to master, I can leave only Shellcheck things and remove unnecessary new input.

Or I can create PR by removing input related changes and leaving all other things.

I'm not sure there is a case when someone would like to output the result into some file, but still wants to see it via results-to-console on console 🤔

[lorenzo]

I'll revert

[ViacheslavKudinov]

Thanks a lot for the quick revert! Didn't want to get something useless released when realized the real outcome of another merged PR.