release: Prepare master for next version 39.0.0-SNAPSHOT

[kfaraz]

Steps

• In root: mvn versions:set -DnewVersion=39.0.0-SNAPSHOT
• In web-console: npm version 39.0.0
• Manually update web-console/unified-console.html to have version

<script src="public/web-console-39.0.0.js"></script>

• Manually update distribution/docker/docker-compose.yml to have version apache/druid:39.0.0 for each Druid container

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This PR has:

• been self-reviewed.
  • using the concurrency checklist (Remove this item if the PR doesn't have any relation to concurrency.)
• added documentation for new or modified features or behaviors.
• a release note entry in the PR description.
• added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
• added or updated version, license, or notice information in licenses.yaml
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.
• added integration tests.
• been tested in a test Druid cluster.

[kfaraz]

Thanks for the reviews, @cryptoe , @capistrant !