Improve azure front door config

[tobiasdiez]

Add domain www.jabref.org and downloads.jabref.org to azure

1. Create CNAME for afdverify subdomains: https://learn.microsoft.com/en-us/azure/frontdoor/standard-premium/how-to-add-custom-domain#add-a-new-custom-domain
2. Test setup. Redirection config at https://learn.microsoft.com/en-us/azure/frontdoor/front-door-rules-engine-actions?pivots=front-door-standard-premium&tabs=portal#UrlRewrite
3. Maybe change the web app config: https://learn.microsoft.com/en-us/azure/static-web-apps/front-door-manual#update-static-web-app-configuration and for azure functions: https://learn.microsoft.com/en-us/samples/azure/azure-quickstart-templates/front-door-standard-premium-function-public/
4. Create CNAME for production subdomains: https://learn.microsoft.com/en-us/azure/frontdoor/standard-premium/how-to-add-custom-domain#associate-the-custom-domain-to-your-front-door-endpoint
5. Change links in readme etc
6. Restrict access to use front door https://learn.microsoft.com/en-us/azure/frontdoor/origin-security?tabs=app-service-functions&pivots=front-door-standard-premium, similar service doesn't yet exist for static web app Azure/static-web-apps#1158

Reference for advanced subdomain handling: nuxt/nuxt#16142, https://zernonia.keypress.blog/why-keypress, https://github.com/zernonia/keypress