WX-1633 Streamline, enhance debug image

[aednichols]

Description

After using it in practice for a while, here's a small round of changes:

• Remove JDK. This was by far the largest by megabytes and the most fickle build process. It was really only there in case I wanted to use jstack as a backup if I couldn't connect YourKit; but we now have a blessed procedure to run YourKit in any environment.
• Message-of-the-day on container login. Enhanced situational awareness to make sure you're on the container you want, and the container is running the version you think it is.

Without the JDK, the image is 634 MB, only 16% larger than baseline at 547 MB.

MOTD example:

> kubectl exec -it -n terra-dev cromwell1-runner-76f7b5d5df-qpwdl -c cromwell1-runner-app -- bash
Version 88-6e242af-DEBUG built at 2024-05-21 18:07:36
root@cromwell1-runner-76f7b5d5df-qpwdl:/# 

Release Notes Confirmation

CHANGELOG.md

• I updated CHANGELOG.md in this PR
• I assert that this change shouldn't be included in CHANGELOG.md because it doesn't impact community users

Terra Release Notes

• I added a suggested release notes entry in this Jira ticket
• I assert that this change doesn't need Jira release notes because it doesn't impact Terra users

[aednichols]

This added mkdir is not strictly necessary because wget would create it for us; but makes it clear that we are manually creating this folder for ourselves, rather than being some kind of built-in Docker magic.