Use supported version of Node.js in Dockerfile

[trivikr]

The Dockerfile in superset-websocket uses Node.js 16.x which was end-of-life on 2023-09-11

superset/superset-websocket/Dockerfile

Line 15 in cc1bb69

FROM node:16-alpine as build

Use supported version of Node.js in Dockerfile.
The latest LTS version at the time of comment is Node.js 20.x