Update java templates in rbeconfigsgen.go

[hvadehra]

Uses @rules_java for bazel > 7.0.0 (including pre-releases)

• Added tests for java template resolution, but I can't seem to find any reference to that file. Is that configured somewhere in CI or only meant for manual runs?
• I've made sure to preserve existing behavior as much as possible. The only difference is if --bazel_version is not passed, we use the latest template.
• I'm not happy about the naming of the templates, but I plan to clean this once support for 4.0.0 is dropped in Jan 2024, and we can bring down the number of java templates to 2.