Unable to set scope field for role assignments

[SenthuranSivananthan]

Bicep version
Bicep CLI version 0.2.59 (5b0314c)

Describe the bug
I'm not able to assign roles to resources using Bicep. The use case is to assign Blob Data Contributor role to Azure Data Factory.

Error

Error BCP038: The property "scope" is not allowed on objects of type "Microsoft.Authorization/roleAssignments". Permissible properties include "dependsOn".

To Reproduce

param storageAccountPrefix string = 'stg'
param dataFactoryName string = 'adf'

var storageBlobDataContributorRoleId = 'ba92f5b4-2d11-453d-a403-e96b0029c9fe'

resource stg 'Microsoft.Storage/storageAccounts@2019-06-01' = {
  location: resourceGroup().location
  name: '${storageAccountPrefix}${uniqueString(resourceGroup().id)}'
  kind: 'StorageV2'
  sku: {
    name: 'Standard_LRS'
  }
  properties: {
    accessTier: 'Hot'
    supportsHttpsTrafficOnly: true
  }
}

resource adf 'Microsoft.DataFactory/factories@2018-06-01' = {
  location: resourceGroup().location
  name: '${dataFactoryName}'
  identity: {
    type: 'SystemAssigned'
  }
}

resource adfToStgRoleAssignment 'Microsoft.Authorization/roleAssignments@2020-04-01-preview' = {
  name: guid(resourceGroup().id)
  **scope: stg.id**
  properties: {
    principalId: adf.identity.principalId
    roleDefinitionId: resourceId('Microsoft.Authorization/roleDefinitions', storageBlobDataContributorRoleId)
  }
}

Additional context
Scope is a valid attribute per ARM template reference: https://docs.microsoft.com/en-us/azure/templates/microsoft.authorization/roleassignments

[alex-frankel]

The work to enable this is tracked by #870. Going to close this since we are tracking it there.