feat: add skip tls flag for private git context

[schwannden]

Description

If git clone context is a private self-signed repository, we allow user to add --git insecure-skip-tls=true flag in the option. The value is default to false, this behavior is in accordance with the go-git package.

Submitter Checklist

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• Includes unit tests

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Reviewer Notes

• The code flow looks good.
• Unit tests and or integration tests added.

Release Notes

- kaniko adds a new flag `--git insecure-skip-tls` to support private git context

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[aaron-prindle]

@schwannden can you rebase, there was an issue @ HEAD that was recently fixed (this should resolve the test error you are seeing)

[schwannden]

@schwannden can you rebase, there was an issue @ HEAD that was recently fixed (this should resolve the test error you are seeing)

@aaron-prindle done

[schwannden]

@JeromeJu any update?

[aaron-prindle]

LGTM, thanks for the PR here @schwannden!