Added production keyvault signing credentials

For production releases to Azure, instead of using Developer Signing Credentials for issuing JWT access tokens, the API will now expect a certificate that is loaded from Azure KeyVault.

The new configuration settings to add are:

{
  "name": "AzureKeyVault__CertificateName",
  "value": "signing-cert-name",
  "slotSetting": false
},
{
  "name": "AzureKeyVault__AzureTenantId",
  "value": "tenantid",
  "slotSetting": false
}