DCJ-400: Update to java 21

[rushtong]

Addresses

https://broadworkbench.atlassian.net/browse/DCJ-400

Summary

• Similar to [DCJ-400-docker]: Bump broad-dsp-gcr-public/base/jre from 17-debian to 21-debian in the docker-dependencies group consent#2345
• Updates broad-dsp-gcr-public/base/jre from 17-debian to 21-debian
• Update base image, build image, smoke tests, and docs to match latest java version available.

Testing

Testing requires installing java 21 locally and ensuring that your local compose file is updated as well:

app:
  image: us.gcr.io/broad-dsp-gcr-public/base/jre:21-debian

The app should start up and run with no regressions.

---

Have you read CONTRIBUTING.md lately? If not, do that first.

• Label PR with a Jira ticket number and include a link to the ticket
• Label PR with a security risk modifier [no, low, medium, high]
• PR describes scope of changes
• Get a minimum of one thumbs worth of review, preferably two if enough team members are available
• Get PO sign-off for all non-trivial UI or workflow changes
• Verify all tests go green
• Test this change deployed correctly and works on dev environment after deployment

[aarohinadkarni]

manually tested with local jvm update, looks good 👍

[fboulnois]

lgtm 👍