Fix bounce issue with Safari

docs/example-advanced.nginx.conf

@@ -104,6 +104,7 @@ server {
     # Enable SharedArrayBuffer in Firefox (for .xlsx export)
     add_header Cross-Origin-Resource-Policy cross-origin;
     add_header Cross-Origin-Embedder-Policy require-corp;
+    add_header Referrer-Policy same-origin;
 
     # Insert the path to your CryptPad repository root here
     root /home/cryptpad/cryptpad;

lib/defaults.js

@@ -57,6 +57,7 @@ Default.httpHeaders = function (Env) {
         "X-XSS-Protection": "1; mode=block",
         "X-Content-Type-Options": "nosniff",
         "Access-Control-Allow-Origin": Env.enableEmbedding? '*': Env.permittedEmbedders,
+        "Referrer-Policy": "same-origin",
         "Permissions-policy":"interest-cohort=()"
     };
 };