Auto scaling up and down number of partitions

Currently Pulsar has all the mechanisms to change the number of partitions through admin REST api. Sometimes it might be easier if Pulsar provides some policies to auto-scale up and down number of partitions. The scale up and down can be based on policies.

Start by reviewing Pulsar's existing partition-management mechanisms through the admin REST API and the issue's proposed scaling policies. The issue does not name files, tests, triggers, or completion criteria; the work would need those policies and their behavior defined before implementation can be considered done.

Written by the indexing model from the issue text.