This PR adds a upgrade notes and changes examples to use the bootstrap-server.

Author: Viktor Somogyi-Vass <viktorsomogyi@gmail.com>

Reviewers: Srinivas <srinivas96alluri@gmail.com>, Manikumar Reddy <manikumar.reddy@gmail.com>

Closes #6118 from viktorsomogyi/topiccommand-adminclient-doc