Deploy postgresql using getSecret()

postgresql.bicep

@description('key vault name')
param keyVaultName string
@description('secret name for db admin user')
param userSecretName string
@description('secret name for db admin password')
param passwordSecretName string

resource kv 'Microsoft.KeyVault/vaults@2019-09-01' existing = {
  name: keyVaultName
}

resource pgsql 'Microsoft.DBForPostgreSQL/servers@2017-12-01' = {
  name: name
  location: location
  sku: {
     ...
  }
  properties: {
    createMode: 'Default'
    administratorLogin: kv.getSecret(userSecretName)
    administratorLoginPassword: kv.getSecret(passwordSecretName)
  }
}