Redirect to new jupyter notebook project

[sergioferragut]

Description

We've moved the jupyter notebook examples that are present here to a separate project.
This change just notifies users of the new github repository at https://github.com/implydata/learn-druid

This PR has:

• [ x ] been self-reviewed.
  • using the concurrency checklist (Remove this item if the PR doesn't have any relation to concurrency.)
• [ x ] 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.

[317brian]

There are references to notebooks in docs/tutorials/ too:

https://github.com/apache/druid/blob/master/docs/tutorials/tutorial-jupyter-index.md
https://github.com/apache/druid/blob/master/docs/tutorials/tutorial-jupyter-docker.md

[techdocsmith]

There are references to notebooks in docs/tutorials/ too:

master/docs/tutorials/tutorial-jupyter-index.md master/docs/tutorials/tutorial-jupyter-docker.md

I'll clean these up: #15143