Describe SASL option for KafkaSource

[matzew]

Describe the change you'd like to see

I do not see any SASL related documentation in the kafka source docs: https://knative.dev/development/developer/eventing/sources/kafka-source/

However, the Source does support SASL in various ways, and it should be documented.

Some comments on the relevant bits are in here: https://github.com/knative-sandbox/eventing-kafka/pull/237#issuecomment-734721870

Ideally we have some doc that describe the following section, for SASL:

...
net:
  sasl:
   enable: true
   user:
      secretKeyRef:
        name: strimzi-sasl-secret
        key: user
    password:
      secretKeyRef:
        name: strimzi-sasl-secret
        key: password
    saslType:
      secretKeyRef:
        name: strimzi-sasl-secret
        key: saslType
...

[github-actions[bot]]

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.

[github-actions[bot]]

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.

[jmcx]

Suggesting to reopen this issue, we've struggled to implement this given the lack of documentation. cc @odacremolbap