nginx: Add support for large files in restconf app.

board/common/rootfs/etc/nginx/restconf.app

@@ -1,5 +1,11 @@
 # /telemetry/optics is for streaming (not used atm)
+# Proxy buffer settings for large files
+proxy_buffering off;                 # Disable buffering for streaming
+proxy_request_buffering off;         # Stream request body immediately
+proxy_max_temp_file_size 0;         # No temp files
 location ~ ^/(restconf|yang|.well-known)/ {
+    client_max_body_size 200M;
+    client_body_buffer_size 1M;
     grpc_pass grpc://[::1]:10080;
     grpc_set_header Host $host;
     grpc_set_header X-Real-IP $remote_addr;