201-web-app-certificate-from-key-vault and passwords

[201-web-app-certificate-from-key-vault](https://github.com/Azure/azure-quickstart-templates/blob/master/201-web-app-certificate-from-key-vault/azuredeploy.json)

### Issue Details
According to the [docs](https://docs.microsoft.com/en-us/azure/templates/microsoft.web/2018-02-01/certificates#certificateproperties-object), the `Password` field is required, yet none of the samples using Keyvault sets the password. Are the templates wrong, or the docs?

Start with 201-web-app-certificate-from-key-vault/azuredeploy.json and compare its certificate password handling with the linked Microsoft.Web certificate properties documentation. Determine whether the Key Vault sample or the documentation is inconsistent, then update the relevant template or documentation and verify the result against the other Key Vault samples.

Written by the indexing model from the issue text.