missing metadata host URL on backend configurations

[glennmusa]

Description

The codebase supports specifying a different management endpoint (e.g. "management.azure.com" or "management.usgovcloudapi.net") for Terraform variables, but it does not use that endpoint to instantiate a backend.

Steps to Reproduce
Steps to reproduce the behavior:

1. Specify a non-commercial endpoint
2. Attempt to apply or init Terraform into a non-commercial storage account

Expected behavior
I should be able to init and apply Terraform with supported endpoints. We should pass the endpoint as a backend-config argument here:

missionlz/src/scripts/apply_terraform.sh

Lines 65 to 74 in 08eae8e

	terraform init \
	-backend-config "key=${key}" \
	-backend-config "resource_group_name=${tf_be_rg_name}" \
	-backend-config "storage_account_name=${tf_be_sa_name}" \
	-backend-config "container_name=${container_name}" \
	-backend-config "environment=${environment}" \
	-backend-config "tenant_id=${tenant_id}" \
	-backend-config "subscription_id=${sub_id}" \
	-backend-config "client_id=${client_id}" \
	-backend-config "client_secret=${client_secret}"

Actual behavior
Initialization fails with Error: unable to locate metadata for environment "<envrionment name>" from the built in "public", "usgovernment", "china" and no customer metadata host has been specified

Additional context
Operating System:
Terraform Version:
Cloud (public, Azure Government, etc.):