refactor hcl parser / update commands&outputs for options docs

[boranx]

I've just gone through the documentation and found some outdated areas.
This PR updates the documentation

[jpreese]

I think it would better showcase the input flag if the input in the example wasn't the default behavior. If conftest sees a .hcl or .tf file, -i hcl is to be assumed (which is now the hcl2 parser).

I would actually love to see us renaming the terraform parser to hcl, because thats what its really doing.

Then in the examples, we could have hcl and/or hcl2 and/or terraform-hcl1 and/or terraform-hcl2. Not advocating for every single combination, but thats the idea anyway. HCL and HCL2 being the things we parse, and Terraform being an example, but Terraform can be written using HCL1 or HCL2.

[boranx]

generally agreed, but better to rename terraform to hcl1 instead of hcl. Because the hcl input references to the hcl2. Using hcl here could be confusing

[jpreese]

Thanks for putting this together, @boranx!

[boranx]

hi @jpreese

so the changes so far:

• terraform parser is replaced with hcl1
• testdata/ folder has been removed
• docs are updated(current version is not working since we don't have hcl2 folder anymore)
• unknown_extension folder has been created to show the input flag can be used with unknown file types