Remove support for Java 8

[Akshat-Jain]

Description

Starting with Apache Druid 32.0.0, we want to remove the support for Java 8. This PR does that as follows:

• All JDK 8 based CI checks have been removed.
• Images used in Dockerfile(s) have been updated to Java 17 based images.
• Documentation has been updated accordingly.

Release note

Starting with Apache Druid 32.0.0, support for Java 8 has been removed.

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This PR has:

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

[clintropolis]

it looks like java 17 is still running in the second phase of unit tests, these can be removed i think since they replaced the java 8 tests in phase 1, https://github.com/apache/druid/blob/master/.github/workflows/unit-and-integration-tests-unified.yml#L165 (i think this should just be 11 and 21 now)

[Akshat-Jain]

@clintropolis Makes sense, have made the change.