new environment vars for external druid and kafka + jupyter template

[sergioferragut]

Description

The goal of this PR is to parameterize the hostnames for the Kafka and Druid instances such that the jupyter lab environment and its set of notebooks can run on against a variety of deployments. It also standardizes how notebooks are created such that they make use of these environment variables when connecting to Kafka or Druid.

Adjusted the docker compose files to use defaults for
DRUID_VERSION -> defaults to 26.0
DRUID_HOST -> defaults to "router" which works with Druid deployed with the docker compose
KAFKA_HOST -> defaults to "kafka" which works with Kafka deployed with docker compose

Also added a jupyter notebook template @`examples/ that shows how to initialize both kafka and druid host variables in order to make the notebooks work with this parameterized hosts approach.

Using these variables users can use the notebooks on other instances of Druid and/or Kafka.
Examples:

• If you run both Kafka and Druid standalone in the local system and only run jupyter through docker compose:
  KAFKA_HOST=host.docker.internal DRUID_HOST=host.docker.internal docker compose --profile jupyter up -d
• If you run Druid standalone in the local system and run kafka and jupyter through docker compose:
  DRUID_HOST=host.docker.internal docker compose --profile kafka-jupyter up -d
• Self-contained startup with all services running:
  docker compose --profile all-services up -d

This PR has:

• [ x ] 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
• [ x ] 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.
• [ x ] been tested in a test Druid cluster.

[techdocsmith]

nit

[techdocsmith]

LGTM