chore(deps): update node docker tag to v21 (dockerfile)

Dockerfile

@@ -7,7 +7,7 @@
 # docker tag hello-world-rest:local cloudkats/hello-world-rest:local
 # docker push cloudkats/hello-world-rest:local
 ###
-FROM node:18-alpine@sha256:c7620fdecfefb96813da62519897808775230386f4c8482e972e37b8b18cb460
+FROM node:21-alpine@sha256:db8772d9f5796ac4e8c47508038c413ea1478da010568a2e48672f19a8b80cd2
 
 # Create app directory
 WORKDIR /usr/src/app