Terraform/HCL syntax

[mfinelli]

I'm not sure that I've done this correctly, but I grabbed the terraform/hcl syntax highlighting from here: https://github.com/SublimeText/Terraform

This would close #1981

Sanity check:

• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Code changes

(Delete or ignore this section for documentation changes)

• Are you doing the PR on the next branch?

If the change is a new feature or adding to/changing an existing one:

• Have you created/updated the relevant documentation page(s)?

I'm not sure if there is any documentation that needs to be updated