Default client in KafkaBaseHook

[riccardoforzan]

Moving the definition of AdminClient as the default client for KafkaBaseHook
Closes: #40204

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[boring-cyborg]

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[boring-cyborg]

Awesome work, congrats on your first merged pull request! You are invited to check our Issue Tracker for additional contributions.

[potiuk]

Thanks! Good first PR :)