fix: client/Dockerfile to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-DEBIAN11-DB53-2825168
- https://snyk.io/vuln/SNYK-DEBIAN11-GLIBC-5927133
- https://snyk.io/vuln/SNYK-DEBIAN11-GLIBC-5927133
- https://snyk.io/vuln/SNYK-DEBIAN11-ZLIB-6008961
- https://snyk.io/vuln/SNYK-UPSTREAM-NODE-5848038

client/Dockerfile

@@ -1,4 +1,4 @@
-FROM node:18.14-slim
+FROM node:21.5-bookworm-slim
 
 LABEL version="1.0"
 LABEL description="Demo of a Medicare claims data sample app"