Deriving java version from release list (issue #18)

[greylurk]

Issue #18 calls out that Java 16 and higher isn't supported by the $ asdf list-all graalvm command, and in fact that command returns entries which are not currently available (i.e. 22.1.0-java8). This update should provide a list of the graalvm releases that are available, along with the OpenJDK versions that are supported by them.

In addition to supporting Java 16+, this also addresses an issue where the list all command would return items which weren't available for the architecture of the current machine (i.e. Apple Silicon). This addresses that as well.