Add unattended terraform execution, centralize Service Principal check, exit on any errors

[glennmusa]

Description

See build/README.md on how to execute/demo this.

As of this writing, round-trip apply/destroy for everything under src/core takes ~35 minutes (most of it on Azure Firewall apply).

Changes:

1. Adds apply_tf and destroy_tf

   These two scripts automate what a human currently does to deploy the terraform configurations at src/core in the repository.

   • The execution of these scripts assume that MLZ Configuration Resources have already been created as a MLZ Configuration file is passed as an argument. In a CI/CD scenario we would write this config file at execution time from known values.
   • The execution of these scripts require valid globals.tfvars and tier-X.tfvars as they are passed in as arguments. Today these are well known and stored outside of the repository. In a CI/CD scenario we would pull these files from some storage.

2. Adds scripts/config/get_sp_identity.sh

   This script validates that Service Principal used by Terraform is available in the MLZ Configuration Resources Key Vault before attempting to use it to invoke terraform and deploy resources.

   • see apply_terraform.sh L60 for how it's used
   • see destroy_terraform.sh L60 for how it's used
   • see init_terraform.sh L45 for how it's used

3. Prepends all shell scripts in the solution with set -e

   • any error or non-zero exit code returned by scripts in this repo or any execution that this repo invokes (like Azure CLI and Terraform CLI) will exit the calling script immediately.

Issue reference

The issue this PR will close: #16, #62

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles or validates correctly
• BASH scripts have been validated using shellcheck
• All tests pass (manual and automated)
• The documentation is updated to cover any new or changed features
• Markdown files have been linted using the recommended linter. (See .vscode/extensions.json.)
• Relevant issues are linked to this PR