Update deprecation notice

[coignetp]

What does this PR do?

Some consumers (like HighLevelConsumer) used to store and fetch offset from Zookeeper. This is deprecated and the supported way is to fetch offset from kafka brokers.

https://www.confluent.io/blog/tutorial-getting-started-with-the-new-apache-kafka-0-9-consumer-client/
A customer asked for clarification about this deprecation note.

Motivation

Additional Notes

Config specs added #8108, let's be careful not to override the note update

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• PR must have changelog/ and integration/ labels attached

[codecov]

Codecov Report

Merging #8161 (8ddb471) into master (e986b41) will decrease coverage by 7.22%.
The diff coverage is n/a.

Impacted Files	Coverage Δ
...er/datadog_checks/kafka_consumer/kafka_consumer.py	73.93% <ø> (ø)
amazon_msk/datadog_checks/amazon_msk/__init__.py
ibm_mq/tests/conftest.py
cilium/tests/conftest.py
...tadog_checks_dev/datadog_checks/dev/tooling/git.py
etcd/tests/conftest.py
confluent_platform/tests/conftest.py
...ool/datadog_checks/cassandra_nodetool/__about__.py
...atadog_checks/base/checks/prometheus/base_check.py
haproxy/datadog_checks/haproxy/legacy/const.py
... and 876 more