Bump node from 16 to 21

Bumps node from 16 to 21.

---
updated-dependencies:
- dependency-name: node
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

Dockerfile

@@ -1,5 +1,5 @@
 # generate frontend assets
-FROM node:20 as frontend
+FROM node:21 as frontend
 RUN apt-get update \
     && DEBIAN_FRONTEND=noninteractive apt-get install -y -o Dpkg::Options::="--force-confold" --no-install-recommends --no-install-suggests \
         build-essential \