[WIP]Record unused schema ledgers to ZK for partitioned topics

[BewareMyPower]

Motivation

When creating schema for a partitioned topic, e.g. my-topic, only one z-node /schemas/public/default/my-topic would be created to record the schema's metadata. However, multiple ledgers would be created because each single partition would try to create the schema: first append a ledger, then write the same z-node.

#2959 and #6683 solved the race condition of accessing the same z-node by calling putSchema() again. However, the unused ledgers of other partitions were created and were not recorded in the z-node. So, there's no way to locate these ledgers from ZK, which means there's no way to delete a topic's all associated schema ledgers.

Modifications

• Record these unused ledgers' id under the topic's z-node, e.g. /schemas/public/default/my-topic/unusedLedgers/0 for topic my-topic and ledger 0.
• Add a unit test to check if unusedLedgers z-node has these ledgers' id and these ledgers exist, after a partitioned topic's schema was created.
• Make BookkeeperSchemaStorage.delete() delete ledgers found from ZK, instead of recording ledgers in memory.

Verifying this change

• Make sure that the change passes the CI checks.

This change added tests and can be verified as follows:

Run test PartitionedTopicsSchemaTest.testUnusedLedgers.

[BewareMyPower]

/pulsarbot run-failure-checks

[BewareMyPower]

/pulsarbot run-failure-checks

[BewareMyPower]

Close this PR first because it's a temporary solution for current schema design. After discussing with @codelipenghui , the schema storage design should change, then this PR may not be needed.