Update Code to 1.90.0 (#6824)

Additionally:

- Update Node to 20.11.1
- Update documentation
- Disable extension signature verification

This works around an issue where the Open VSX is not returning the
expected zip.  Verification is skipped later anyway because
@vscode/vsce-sign is missing in the OSS version.

ci/build/npm-postinstall.sh

@@ -76,8 +76,8 @@ main() {
     echo "USE AT YOUR OWN RISK!"
   fi
 
-  if [ "$major_node_version" -ne "${FORCE_NODE_VERSION:-18}" ]; then
-    echo "ERROR: code-server currently requires node v18."
+  if [ "$major_node_version" -ne "${FORCE_NODE_VERSION:-20}" ]; then
+    echo "ERROR: code-server currently requires node v20."
     if [ -n "$FORCE_NODE_VERSION" ]; then
       echo "However, you have overrided the version check to use v$FORCE_NODE_VERSION."
     fi