Java SDK: Increase Gradle daemon heap to fix OOM when building from source

[mjameswh]

Summary

• Adds gradle.properties to set org.gradle.jvmargs=-Xmx2g -XX:MaxMetaspaceSize=512m
• Without this, the Gradle daemon uses its default 512 MB heap, which is insufficient when building the Java SDK from source via a composite includeBuild
• Triggered by Update Temporal Cloud-API to v0.12.0 sdk-java#2814, which adds more protobuf definitions and pushes compilation of temporal-serviceclient past the default heap limit on the ubuntu-latest runner
• Also, bump Java to 23.

Context

When the Java features test runs with version-is-repo-ref: true, sdkbuild/java.go uses Gradle's includeBuild to composite-build the full sdk-java repo. The gradlew invoked is the one from the features repo root, so this gradle.properties controls the daemon heap for the entire build (including the included sdk-java subproject).

The sdk-java repo's own CI doesn't hit this because it uses ubuntu-latest-16-cores runners and gradle/actions/setup-gradle@v5 caching, whereas the features workflow starts a fresh daemon on ubuntu-latest with no memory configuration.

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