[Module Proposal]: `avm-ptn-alz-policy-exemptions`

### Check for previous/existing GitHub issues/module proposals

- [x] I have checked for previous/existing GitHub issues/module proposals.

### Check this module doesn't already exist in the module indexes

- [x] I have checked for that this module doesn't already exist in the module indexes.

### Bicep or Terraform?

Terraform

### Module Classification?

Pattern Module

### Module Name

avm-ptn-alz-policy-exemptions

### Module Details

This module would be used to manage policy exemptions across an entire tenant or a part of a tenant, aligned to Azure Landing Zones.

The exact details of the implementation are to be decided, but want to add a placeholder.

### Do you want to be the owner of this module?

Yes

### Module Owner's GitHub Username (handle)

jaredfholgate

### (Optional) Secondary Module Owner's GitHub Username (handle)

matt-FFFFFF