v3 API should be able to retrieve testimage artifacts for a certain release

[jerboaa]

Binary Type already has jre and jdk as possible values. A third possible value of testimage comes to mind for retrieving the test image which can then be used for testing.

PR adding testimage artifacts:
adoptium/temurin-build#1251

Examples:
https://ci.adoptopenjdk.net/job/build-scripts-pr-tester/job/build-test/job/jobs/job/jdk11u/job/jdk11u-linux-x64-hotspot/133/
https://github.com/AdoptOpenJDK/openjdk11-upstream-binaries/releases/tag/jdk-11.0.5%2B5

Note: testimage artifacts are JDK 11+ only.

[johnoliver]

should be working