Update kafka consumer consumer_groups_regex example to be more inform…

[yzhan289]

…ative

What does this PR do?

This PR updates the example used in consumer_groups_regex to be more realistic in how the option can be used.

Motivation

#14382 (comment)

Additional Notes

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
• If the PR doesn't need to be tested during QA, please add a qa/skip-qa label.

[codecov]

Codecov Report

Merging #14533 (66f37b2) into master (ccc8074) will not change coverage.
The diff coverage is n/a.

Flag	Coverage Δ
kafka_consumer	93.43% <ø> (ø)

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