Update Apache mirror host to downloads.apache.org

[Akshat-Jain]

Description

We currently point APACHE_ARCHIVE_MIRROR_HOST to https://archive.apache.org/.

https://archive.apache.org/dist/ says the following: THEY MAY BE UNSUPPORTED AND UNSAFE TO USE. Current releases can be found on our download server. (download server being https://downloads.apache.org/)

We had a lot of flaky standard ITs because of transient networking issues, which were surfacing as Error while posting dynamic config errors because of a bug introduced recently, discussed here.

While switching to https://downloads.apache.org doesn't seem to solve the flakiness issue (as one of the standard ITs on this PR is still failing with Error while posting dynamic config error because of exhausting all 3 retries for running base-setup.sh), we should move to it as it's recommended, and might potentially help reduce flakiness to some extent.

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This PR has:

• been self-reviewed.
• 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.