Investigate swapping JDK for JRE in elk stack container

[SwooshyCueb]

With #26, we are now using Temurin's JDK instead of the JDK/JRE provided by the distribution or the JDK/JRE bundled with elasticsearch.

The decision not to use elasticsearch's bundled JDK/JRE was made for two reasons:

• To de-bloat the container image. Having multiple JDK/JRE installations uses a lot of space.
• To get everything using the same JDK/JRE

Temurin was chosen over the distro-provided JDK/JRE for a few reasons:

• The Hotspot AdoptOpenJDK flavor of JVM handles memory pressure very well.
• The AdoptOpenJDK flavors of JVM work well in containers.
• I've just generally had better experience with AdoptOpenJDK flavors of JVM than any others.

Given that we are no longer installing plugins in logstash, it is likely that we do not need a full JDK. However, after the AdoptOpenJDK working group was absorbed into the Eclipse foundation and became Adoptium, JRE-only packages (and OpenJ9 packages) were no longer provided in the apt repositories. Eclipse provides a focal-based docker image containing JRE-only Temurin 17 _[Dockerfile], but it is not set up to work properly with Ubuntu's java-common system so it cannot be used. Fortunately, Adoptium has a couple of blog posts that might help us out:

• https://blog.adoptium.net/2021/08/using-jlink-in-dockerfiles/
• https://blog.adoptium.net/2021/10/jlink-to-produce-own-runtime/

[SwooshyCueb]

More rationale for doing this: Adoptium's apt repository is hosted behind a cloudflare gateway, which will sometimes block attempts to download the package from within a container.