e2e: add terraform lockfile

Terraform v0.14 is producing a lockfile after running `terraform init`.
The docs suggest we should include this file in the git repository:

> You should include this file in your version control repository so
> that you can discuss potential changes to your external dependencies
> via code review, just as you would discuss potential changes to your
> configuration itself.

Sounds similar to go.sum

https://www.terraform.io/docs/configuration/dependency-lock.html#lock-file-location