Add new step for Dockerfile linting (#723)

* Add new step for Dockerfile linting

* Add documentation template file

* Remove newlines

* Remove internal URL

* Rephrase comment

* Ammend stash

* Fix test

* move dockerImage to general

* use explicit curl options

* small changes

* small changes

* skip GIT blame

* First comments

* Also add remark to URL parameter

* Second set of comments

* Fix return code handling

* Switch type to set

* Revert unrelated changes

* Avoid modification of config

* add quality gate defaults

* Update hadolintExecute.groovy

* fix code climate issue

documentation/docs/steps/hadolintExecute.md

@@ -0,0 +1,17 @@
+# ${docGenStepName}
+
+## ${docGenDescription}
+
+## ${docGenParameters}
+
+## ${docGenConfiguration}
+
+## Exceptions
+
+None
+
+## Examples
+
+```groovy
+hadolintExecute script: this
+```