topic counts.
Introduces the use of persistent data structures in the KRaft metadata image to avoid copying the entire TopicsImage upon every change. Performance that was O(<number of topics in the cluster>) is now O(<number of topics changing>), which has dramatic time and GC improvements for the most common topic-related metadata events. We abstract away the chosen underlying persistent collection library via ImmutableMap<> and ImmutableSet<> interfaces and static factory methods.
Reviewers: Luke Chen <showuon@gmail.com>, Colin P. McCabe <cmccabe@apache.org>, Ismael Juma <ismael@juma.me.uk>, Purshotam Chauhan <pchauhan@confluent.io>