Upgrade Gradle to support java 17 build

While running the JAR file works with the latest LTS Java version (17), the gradle-based build does not. We need to upgrade gradle to at least 7.3 to support building with 17. Potentially upgrade further in anticipation of new java 23 release in the fall.

https://docs.gradle.org/current/userguide/upgrading_version_6.html
