[AVM Module Issue]: avm/res/app/managed-environment | Key Vault Certificates

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### Issue Type?

Feature Request

### Module Name

avm/res/app/managed-environment

### (Optional) Module Version

_No response_

### Description

Hi there!

Currently when referencing a key vault certificate we have to provide a managed identity resource ID, but how is that supposed to work when we are deploying the managed environment, attempting to set certificates, using the managed environments system assigned ID.

I would like to request support for using the system assigned managed identity rather than a user assigned with resource ID. Right now it will have to be like a post deployment script from what I am seeing with the AVM module.

Thanks!

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