[RJA-2226][[RJA-2227][feature] - Attachment objects for step results

Example usage in step executor:

```scala
class RunLocalActionExecutor(val action: RunLocalShell, shellService: LocalShellExecutionService) extends SyncActionExecutor {
  def startSync() = {
    val result = shellService.exec(action.shell, action.command, action.outputDirectory, Option(action))
    new RunLocalResult(action, result, Seq(FileAttachable("/etc/passwd")))
  }
}



case class RunLocalResult(action: RunLocalShell, response: ExecResponse, attachments: Seq[Attachable]) extends ActionResultWithDesc with ResultWithAttachment {
    override def outcome = if (response.exitCode == action.expectedExitCode)
        Succeed
    else
        Failed
}
```