KafkaChannel reconciler creates Kafka client too often

[aliok]

Describe the bug
KafkaChannel reconciler creates Kafka client too often. ...in every reconciliation loop.
Storing the client and reusing breaks things. See discussion here: #886 (comment)

Expected behavior
Not too many Kafka clients created

To Reproduce
See discussion here: #886 (comment) and apply the reverted change.

Knative release version
0.24, 0.25, 0.26

Additional context
See discussion here: #886 (comment)

[github-actions]

This issue is stale because it has been open for 90 days with no
activity. It will automatically close after 30 more days of
inactivity. Reopen the issue with /reopen. Mark the issue as
fresh by adding the comment /remove-lifecycle stale.

[pierDipi]

/remove-lifecycle stale
/triage accepted