Microsoft.Web/Sites

**Bicep version**
0.4.1

**Describe the bug**
The property "metadata" is not allowed on objects of type "SiteConfig".

**To Reproduce**
```
resource site 'Microsoft.Web/sites@2021-01-01' = {
name: 'site'
location: 'west europe'
kind: 'app'
properties: {
enabled: true
siteConfig: {
metadata: [
{
name: 'CURRENT_STACK'
value: 'dotnetcore'
}
]
}
}
}
```

It compiles and works but it does give a warning: Warning BCP037

Start with the reproduction using Bicep 0.4.1 and the Microsoft.Web/sites@2021-01-01 resource shown in the issue. Locate the SiteConfig type definition for Microsoft.Web/Sites and compare its supported properties with the example; done means the metadata property is accepted without warning and the resource still compiles.

Written by the indexing model from the issue text.