This addresses https://linear.app/comm/issue/ENG-8844/make-terraform-config-add-task-def-variables-through-a-env-file
We use a local `.env` file (functionally identical to one we would use in comm/keyserver/.env) to include the env variable for the primary/secondar node ecs tasks
Originally, we were using `terraform.tfvars` to specify the values for these environmental variables and hardcoding a set list of env variables that would be included in our primary/secondary ecs tasks.
The new method allows the user to specify any env variable which will then appear in the ecs task by modifying the `.env` file in `comm/services/terraform/self-host/.env`