az deployment group what-if returns generated changes

**Describe the bug**
When running `az deployment group what-if` on an ARM template, some properties that are typically generated on resource creation pops up as property deletes (i.e. the change set specifies that these properties will be set back to NULL). This happens in several places, the latest example for example is when creating a DataBricks workspace (Microsoft.Databricks/workspaces). In this case the properties are principalId and roleDefinitionId in the authorization properties. I don't set these because the principal is managed by Azure.

**To Reproduce**
Use az deployment group what-if on e.g. a DataBricks workspace template after deploying the same template. There are property changes.

**Expected behavior**
When deploying the same template, there should be zero property changes.

**Environment summary**
azure-cli 2.11.0

core 2.11.0
telemetry 1.0.6

Extensions:
front-door 1.0.9

Python location '/usr/local/bin/python'
Extensions directory '/usr/local/lib/azure-cli-extensions'

Python (Linux) 3.8.6 (default, Dec 17 2020, 02:08:55)
[GCC 9.3.0]

Legal docs and information: aka.ms/AzureCliLegal

**Additional context**
We wrap this command in a Azure DevOps pipeline to detect if an ARM deployment changed and for some resources we want to trigger an approval step in this case. The current operation of this command triggers a log of noise in our pipelines.