Add a `per` export type in the server and generate the PER Country page preparedness tab PDF export

[samshara]

I suggest we also refactor the export endpoint as following
The client sends only the following information

• export_type
• identifier

The server should have a static configuration to save information regarding exports
For example

• client
  • https://go-web-ifrc.dev.datafriendlyspace.org
• DREF export
  • url-format: /dref-applications/{}/export
  • url-selector: '#pdf-preview-ready`

.... and others

1. We also need to support a white list for the client field, as of right now it can be anything as configured in the client.
2. We also need a separate environment variable on the client side to determine if we must use the currently deployed front-end for export. This can be true only for the testing environment.
   The PDF export could have a security vulnerability as explained in https://blog.projectdiscovery.io/abusing-reverse-proxies-metadata/

cc @thenav56