Add GraalVM and Native Image Builder to CodeBuild Image for Java

Building Java Lambdas with GraalVM is a recommended best practice to reduce cold start times, but CodeBuild does not currently include the tools (GraalVM, Native Image Builder) that are required for a customer to use CodeBuild to build native images. Having each customer build their own CodeBuild image to include these tools seems wasteful, and including them in the AWS-supported Java CodeBuild image would not negatively impact customers who aren't using it. Including the tools in the Java CodeBuild image would go a long way to helping customers adopt using GraalVM for their Java Lambdas.

For reference, here are some AWS blog posts talking about using GraalVM for this purpose:

https://aws.amazon.com/blogs/developer/graalvm-native-image-support-in-the-aws-sdk-for-java-2-x/

And an example implementation by an AWS employee is available at:

https://github.com/marksailes/al2-graalvm