feat: add JSON output format for Hadolint report

Christophe Mathiasrequested to merge
christophe_mathias/docker:1-hadolint-report-in-json-format into master

Presentation

Hadolint report is currently generated in Gitlab Code Climate format. In addition to this format which is necessary for Gitlab, it may be useful to get Hadolint report in standard JSON format, in order to import it into a tool like DefectDojo.

Closes #1 (closed)

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