Add Managed Identity AKS Terraform Template to Bedrock Environments

[NathanielRose]

As a:
Developer
I want:
Terraform Template that leverages Managed Identity (MIC) for handling an AKS and nodes

So that:
I can have a boilerplate template for the GA MSI integration with AKS
Describe the solution you'd like:
A new AKS Bedrock template with Managed Identity enabled, (azure-MI), will be
added to the collection of environment templates. This template will be an
upgraded derivative of the azure-simple template, with a new dependency on
azure-common-infra and will contain the following:

• Managed Identity System Level for AKS
• Pod Identity Security Policy
• Backend State

Acceptance Criteria:

• Template uses azurerm provider 2.5
• Pod identity for auth to template app Migrated to [Spike]: [Spike] Investigate Manage Identity AKS interoperability with CSI #1355
• Backend state
• Documentation

Describe alternatives you've considered:
Reference Design Document: https://github.com/microsoft/bedrock-cli/blob/master/technical-docs/designs/infra/managed-identity.md

Additional context:
Related to: #1197

Does this require updates to documentation?:
Yes