app service: siteConfig.http20ProxyFlag not recognized

### Resource Type

Microsoft.Web/sites

### Api Version

2022-09-01

### Issue Type

Missing property(s)

### Other Notes

The property that controls the setting **HTTP2.0 Proxy** (under `Configuration --> General Settings` for an app service) incorrectly gets a warning when deploying the .bicep file:

> Warning BCP037: The property "http20ProxyFlag" is not allowed on objects of type "SiteConfig". Permissible properties include...

However, after deploy, the setting is indeed set correctly.

Note that this setting is currently only available on Linux. It is needed when hosting gRPC services in azure: https://github.com/Azure/app-service-linux-docs/blob/master/HowTo/gRPC/use_gRPC_with_dotnet.md

### Bicep Repro

```bicep
resource mainAppService 'Microsoft.Web/sites@2022-09-01' = {
name: 'MyAppWithHttp20Proxy`
location: location
// Display only
kind: 'linux'
properties: {
serverFarmId: appServicePlan.id
// true means linux
reserved: true
httpsOnly: true
siteConfig: {
http20Enabled: true
minTlsVersion: '1.2'
linuxFxVersion: 'DOTNETCORE|7.0'
// This gets incorrectly flagged as invalid, both in vscode and in the CLI (az deployment group create ...)
http20ProxyFlag: 1
}
}
identity: {
type: 'SystemAssigned'
}
}
```

### Confirm

- [X] I have read the troubleshooting guide and looked for duplicates.

Start with the Microsoft.Web/sites@2022-09-01 SiteConfig type definition and reproduce the Bicep warning using the supplied resource. Verify that http20ProxyFlag is accepted for the Linux configuration while the deployment behavior remains unchanged; done means the VS Code and CLI validation warnings are gone.

Written by the indexing model from the issue text.