Environment setup enhancements for Terraform

[dremin]

Summary

• Adds support for specifying an item's parent in mappings.json. This is useful for child objects such as serverless environments and functions, and has retroactively been applied to TR workflows.
• Adds support for new types in mappings.json: serverless-environment, serverless-function, and serverless-service.
• Adds a cache so that results from CLI commands can be reused if needed (serverless-domain makes the same requests as serverless-service and serverless-environment).
• Adds support for specifying individual files to perform environment variable processing on, as well as support for skipping package processing.

The above work was done as a prerequisite to allow reuse of the setup script for populating Terraform variables (used for objects managed outside of Terraform). This is a first step of reducing the complexity of Terraform deployments:

• Modified the import_internal_state.sh script to call the setup script to populate an environment-specific tfvars file
• Modified Terraform config files to use the tfvars file
• Adjusted scripts to use the Twilio CLI installed by the top-level npm package

Checklist

• Tested changes end to end
• Updated documentation
• Requested one or more reviewers

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[jared-hunter]

looks great, i love these improvements