[Microsoft.Network/BastionHosts]: `dnsName` property should be read-only

### Resource Type

Microsoft.Network/BastionHosts

### Api Version

2022-07-01

### Issue Type

Property(s) should be marked as read-only/write-only

### Other Notes

Modifications are displayed in What-if output - however it is a no-op during deploy:

```pwsh
Resource and property changes are indicated with these symbols:
- Delete
~ Modify
= Nochange
* Ignore

The deployment will update the following scope:

Scope: /subscriptions//resourceGroups/

~ Microsoft.Network/bastionHosts/myvnet-bastion [2022-07-01]
- properties.dnsName: "bst-.bastion.azure.com"
```

### Bicep Repro

```bastion
resource bastion 'Microsoft.Network/bastionHosts@2022-07-01' = {
name: 'test-bastion'
location: location
sku: {
name: 'Standard'
}
properties: {
dnsName: 'mycustomfqdn.bastion.azure.com'
ipConfigurations: [
{
id: ipconfigId
properties: {
subnet: {
id: vnetSubnetId
}
}
}
]
}
}
```

### Confirm

- [X] I have searched this repository and have not found similar issue reports.

The payload names Microsoft.Network/BastionHosts version 2022-07-01 but no source file, test, or entry point. Start by locating the type definition for this resource and its dnsName property; done means dnsName is represented as read-only and its attempted change is no longer shown as an effective deployment modification.

Written by the indexing model from the issue text.