OAK-12331: document the audit SPI - #3058

The operation was canceled.

Task org.apache.jackrabbit.oak.commons.concurrent.NotifyingFutureTask@1e6b1e39[Not completed, task = org.apache.jackrabbit.oak.spi.commit.BackgroundObserver$1$1@5d55f05f] rejected from java.util.concurrent.ThreadPoolExecutor@7535a74d[Shutting down, pool size = 1, active threads = 1, queued tasks = 0, completed tasks = 6]

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/setup-java@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/