Add Support for Microsoft.Web/certificates

[tehmufifnman]

Use Case:
We have a private key certificate sitting inside a KeyVault. Its referenced by keyVaultId and keyVaultSecretName properties. When you reference a certificate in this way inside of an ARM template, the sites resource in your ARM template is given a reference to it, which can then be loaded if you have a siteConfig env var called "WEBSITE_LOAD_CERTIFICATES" set to "*" (or a specific name).
See https://docs.microsoft.com/en-us/azure/app-service/configure-ssl-certificate-in-code for details

Sample ARM JSON:

      "apiVersion": "2018-11-01",
      "name": "[parameters('encryptionCertificateName')]",
      "type": "Microsoft.Web/certificates",
      "location": "[resourceGroup().location]",
      "tags": "[parameters('resourceTags')]",
      "dependsOn": [
        "[concat('Microsoft.Web/sites/', parameters('appName'))]"
      ],
      "properties": {
        "keyVaultId": "[parameters('keyVaultId')]",
        "keyVaultSecretName": "[parameters('encryptionKeyVaultSecretName')]"
      }
    }