add interim step to remove bug with diff tf vers

[dilyankostov]

The docker terraform-compliance image packages in it terraform binaries for a specific version (for example image eerkunt/terraform-compliance:1.3.8 has terraform 0.14.0). However when terraform plan is used with a different version (for example 0.13.0), it throws an error: terraform-compliance/cli#273, terraform-compliance/cli#381 . I.e. a user running the commands in this document is likely to get an error unless they are running the version of terraform in the image.
There are two ways of addressing this known to me:

1. Add the terraform binaries for the version 'terraform plan' is using the --terraform flag in the terraform-compliance command Converting terraform plan file. ERROR: Failed to convert terraform plan file to JSON format via terraform terraform-compliance/cli#381
2. Add an intermediate step to convert the execution plan to json and then just supply that file as seen here Converting terraform plan file. ERROR: Failed to convert terraform plan file to JSON format via terraform terraform-compliance/cli#381

This pull request provides the second option as it removes the need to transfer terraform binaries to a docker image.

[ghost]

All CLA requirements met.

[TomArcherMsft]

@eerkunt Thanks for the feedback. As this article has been updated recently, I incorporated the relevant changes into the new article.