Increase max body size for the nginx proxy

Otherwise, we can't support large media file uploads.

roles/matrix-server/templates/nginx-conf.d/matrix-synapse.conf.j2

@@ -15,10 +15,10 @@ server {
 }
 
 server {
-    listen 443 ssl http2;
-    listen [::]:443 ssl http2;
+	listen 443 ssl http2;
+	listen [::]:443 ssl http2;
 
-    server_name {{ hostname_matrix }};
+	server_name {{ hostname_matrix }};
 
 	server_tokens off;
 	root /dev/null;
@@ -30,8 +30,14 @@ server {
 	ssl_prefer_server_ciphers on;
 	ssl_ciphers "EECDH+AESGCM:EDH+AESGCM:AES256+EECDH:AES256+EDH";
 
-    location /_matrix {
-        proxy_pass http://synapse:8008;
-        proxy_set_header X-Forwarded-For $remote_addr;
-    }
+	location /_matrix {
+		proxy_pass http://synapse:8008;
+		proxy_set_header X-Forwarded-For $remote_addr;
+
+		# These are intentionally large.
+		# Note that Synapse enforces its own limits, which are smaller.
+		client_body_buffer_size 25M;
+		client_max_body_size 100M;
+		proxy_max_temp_file_size 0;
+	}
 }