Implement Checkup

[JesseMarkowitz]

CryptPad has a built in Checkup (https://reallylonglocaladdressgoeshere.local/checkup/). There are currently 43 tests. CryptPad wrapper should implement whatever is needed in configuration etc. so that all checkup tests are passed.

NOTE: Passing all checkup tests is required by CryptPad.org to be listed as a public instance.

[chrisguida]

This nginx config was recommended by someone in the cryptpad instance admin matrix room

        server {                                                                 
                listen          443 ssl;                                        
                server_name     pad.example.com sandbox.example.com;                      

                location / {                                                     
                        proxy_pass              http://127.0.0.1:3000;           
                        proxy_set_header        X-Real-IP $remote_addr;          
                        proxy_set_header        Host $host;                      
                        proxy_set_header        X-Forwarded-For $proxy_add_x_forwarded_for;
                        client_max_body_size    500m;                            

                        proxy_http_version      1.1;                             
                        proxy_set_header        Upgrade $http_upgrade;           
                        proxy_set_header        Connection upgrade;              

                        add_header              Strict-Transport-Security        
                                                "max-age=31536000; includeSubDomains" always;
                        proxy_hide_header       Cross-Origin-Resource-Policy;    
                        add_header              Cross-Origin-Resource-Policy cross-origin;
                        proxy_hide_header       Cross-Origin-Embedder-Policy;    
                        add_header              Cross-Origin-Embedder-Policy require-corp;
                }                                                                
        }