fix(webapp): use node:lts image (currently supported till 04/2024)

Context:
https://stackoverflow.com/questions/69394632/webpack-build-failing-with-err-ossl-evp-unsupported
https://nodejs.org/en/about/releases/

webapp/Dockerfile

@@ -1,4 +1,4 @@
-FROM node:latest
+FROM node:lts
 RUN \
   apt-get update \
   && apt-get -y install gettext-base \