Azure Firewall Policy Reverts DNS Config if Not Defined - Intended?

**Bicep version**
run `bicep --version` via the Bicep CLI, `az bicep version` via the AZ CLI or via VS code by navigating to the extensions tab and searching for Bicep

**Describe the bug**
A clear and concise description of what the bug is vs what you expected to happen
We are currently testing firewall polices with Bicep, we ran into an issue where a deployment recently removed out DNS proxy settings after a deployment. Our understanding is bicep would not make a change to align a resource to a template unless deploying in complete mode. Our template is below - DNS behavior is not defined.
```
resource firewallPolicy 'Microsoft.Network/firewallPolicies@2022-11-01' = {
name: name
location: location
tags: tags
properties: {
sku: {
tier: tier
}
transportSecurity: tlsInspection == 'Disabled' ? null : {
certificateAuthority: empty(keyVaultName) ? null :{
name: keyVaultCASecretName
keyVaultSecretId: '${keyVault.properties.vaultUri}secrets/${keyVaultCASecretName}/'
}
}
intrusionDetection: {
mode: intrusionDetectionMode
}
threatIntelMode: threatIntelMode
threatIntelWhitelist: {
fqdns: fqdns
ipAddresses: ipAddresses
}
}
}
```

**To Reproduce**
Steps to reproduce the behavior:

- Deploy a firewall policy
- Manually set the dns proxy setting to on
- Deploy a template with the dns proxy config undefined

**Additional context**
This isn't a _problem_ for us exactly, it just caught us off guard during testing and we're trying to see if this behavior is intended. This happened immediately AFTER a failed deployment, which was stuck.

The report does not name a repository file or test. Start by examining the Microsoft.Network/firewallPolicies@2022-11-01 definition and reproduce the listed deployment sequence with the Bicep or Azure CLI commands; done means establishing whether an undefined DNS proxy setting is reset after deployment and whether the behavior belongs to the type definition or Azure.

Written by the indexing model from the issue text.