Upgrade jetty to 9.4.39.v20210325

[jon-wei]

This PR updates jetty dependencies to version 9.4.39.v20210325, to address the following CVE: https://nvd.nist.gov/vuln/detail/CVE-2021-28165

This PR has:

• been self-reviewed.
• added documentation for new or modified features or behaviors.
• 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.