OpenID Connect support

[fhennig]

Kafka docs for OAuthBearer: https://docs.confluent.io/platform/current/kafka/authentication_sasl/authentication_sasl_oauth.html

Issue checklist

This is a simple checklist of things to bear in mind when creating a new issue.

• Describe the use-case, as far is possible. For instance, using the pattern "As a XXXX, I would like XXXX to be able to do XXXX" helps to identify the feature as well as the problem it is intended to address.
• Indicate an approximate level of importance and urgency.
• Indicate if there is a known work-around until such time as the issue has been implemented.

[fhennig]

The docs state that for a production use, we need to implement callbacks in Java: https://docs.confluent.io/platform/current/kafka/authentication_sasl/authentication_sasl_oauth.html#production-use-of-sasl-oauthbearer

I also found this on SO https://stackoverflow.com/questions/52838251/how-to-implement-oauthbearer-sasl-authentication-mechanism-in-kafka and in a blog post: https://medium.com/egen/how-to-configure-oauth2-authentication-for-apache-kafka-cluster-using-okta-8c60d4a85b43

After discussing with @soenkeliebau we decided that we will not do this for now.