SpringBoot Pulsar authentication param properties cause IllegalStateException with Pulsar Client 3.1.0

The Pulsar authentication is currently configured using a map of auth parameters. However, this avenue is deprecated in Pulsar and instead needs to use an encoded auth parameters string. This commit simply takes the auth params map and converts them to the expected encoded json string of auth parameters.

Resolves https://github.com/spring-projects/spring-pulsar/issues/500

Comment From: onobc

Thank you very much @philwebb