update java in docker (#1615)

Author: KatKovacs1

Dockerfile

@@ -1,7 +1,7 @@
 # renovate: datasource=github-releases depName=microsoft/ApplicationInsights-Java
 ARG APP_INSIGHTS_AGENT_VERSION=3.7.1
 
-FROM hmctspublic.azurecr.io/base/java:17-distroless
+FROM hmctspublic.azurecr.io/base/java:21-distroless
 
 COPY lib/applicationinsights.json /opt/app/
 COPY build/libs/sscs-case-loader.jar /opt/app/