WebApp public certificate not updated after redeploy

[201-web-app-public-certificate](https://github.com/Azure/azure-quickstart-templates/tree/master/201-web-app-public-certificate)

### Issue Details

After changing a certificate in the ARM template it is not updated on a redeploy. See repro steps

### Repro steps (*if necessary, delete otherwise*)
1. Deploy template on Azure (I did from Azure DevOps)
2. Change the certificate in the template [azuredeploy.parameters.json](https://github.com/Azure/azure-quickstart-templates/blob/master/201-web-app-public-certificate/azuredeploy.parameters.json) to a totally different (but valid) blob
3. Redeploy template
4. Certificate still has the old thumbprint value in the Azure portal

After removing the certificate manually and then deploying the template again the new certificate is visible in the portal.

**edit** Above I mention that is is a totally different but valid blob, but it is a refresh of the certificate - so the certificate common name is the same. I could see the thumbprint didn't change - so that is why I know it was not the new certificate.

Start with the 201-web-app-public-certificate template and its azuredeploy.parameters.json file. Deploy it, replace the certificate blob with the refreshed valid certificate, and redeploy to confirm whether the portal still shows the old thumbprint. Done means a redeployment updates the Web App certificate without manual removal.

Written by the indexing model from the issue text.