Add core infra terraform templates

[deniscep]

Add core infra terraform templates

What is being addressed

• Implement a set of terraform templates to create TRE Management core as described in infra diagram

How is this addressed

• Added terraform modules for VNET, Subnets, Keyvault, Firewall, S AppGateway, ACR, private DNS, and API Web App (22 resources and 1 resource group provisioned)
• Subnets are delegated/dedicated as specified in infra
• Private endpoints are provisioned for resources on private link, and private DNS is associated with VNET
• Standardized naming convention to "resource abbreviation"-"prefix"-"environment"-"unique-random-id" (e.g. rg-tre-dev-0001)
• Route table is provisioned and associated with Shared subnet, with default 0.0.0.0 route pointing to firewall
• Added tfvars template with sample defaults

Out of scope for this PR:

• hooking up app gateway to app service (pending decision on deployment implementation)
• no firewall rules are added at this time (pending decision on exceptions)
• deployment/composition service resources are not provisioned (pending decision on Porter)
• Gitea & Nexus are not provisioned (pending decision on ACI vs VM)

Closes 5465 in AzDO

[marrobi]

Added some comments from a quick review of tf on my mobile. Some things might need pushing into other issues.

Have naming conventions been considered?

Great to see this making progress.

[sachinkundu]

TL;DR :D
Looks good if it works.