[improve][metadata] Add partition key resolver support for Oxia index scans

[void-ptr974]

Motivation

Oxia records can be routed with PartitionKey. Native secondary-index scans return primary paths, and some callers can derive the routing key from each returned path. A single scan-level PartitionKey only covers scans scoped to one routing key; it does not cover scans that may span multiple routing keys.

For example, transaction op records are stored under /txn/op/<txnId>-<seq> with PartitionKey(txnId). A scan by segment can return op records for multiple transaction IDs, so each follow-up primary read can use the transaction ID derived from the returned path.

This PR adds an option for passing that per-result routing hint and uses it in transaction metadata index scans.

Modifications

• Add Option.PartitionKeyResolver to derive a concrete PartitionKey from a primary path discovered during a scan.
• Resolve a concrete PartitionKey before Oxia loads each primary record returned by scanByIndex.
• Pass fixed or path-derived routing hints from transaction metadata index scans.
• Add multi-shard Oxia coverage for partition-key-aware index scans.

Verifying this change

• Make sure that the change passes the CI checks.

This change added tests and can be verified as follows:

• Added a multi-shard Oxia test for partition-key-aware index scans.
• ./gradlew :pulsar-metadata:compileTestJava :pulsar-broker:compileJava :pulsar-metadata:checkstyleMain :pulsar-metadata:checkstyleTest :pulsar-broker:checkstyleMain -x :managed-ledger:compileTestJava
• ./gradlew :pulsar-metadata:test --tests org.apache.pulsar.metadata.OxiaPartitionKeyTest

Does this pull request potentially affect one of the following parts:

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

This adds a new metadata-store Option subtype. It does not change existing option behavior, configuration defaults, wire protocol, or metadata format.