[Maven Cleanup] Remove managed-ledger and zk-utils test-jar dependencies when possible (#6513)

Currently, many modules depend on `managed-ledger-test.jar` just because they want to use MockBookkeeper and MockZookeeper.  This made module dependencies hard to understand and track.

This PR introduces a new `testmocks` module and pulls all mocks from managed-ledger tests into the new module.
4 files changed