[Feature] [cdc] Support merge_shards in kafka/pulsar database synchronization

### Search before asking

- [X] I searched in the [issues](https://github.com/apache/paimon/issues) and found nothing similar.

### Motivation

binlog data in the same topic may contain data with the same table name in different database. Provide the merge_shards parameter like Mysql-cdc to avoid table name conflicts.

### Solution

_No response_

### Anything else?

_No response_

### Are you willing to submit a PR?

- [X] I'm willing to submit a PR!

Start by locating the existing MySQL CDC implementation of merge_shards and the Kafka/Pulsar database synchronization entry points. Compare how the parameter avoids table-name conflicts across databases, then define the affected synchronization paths and tests; done means merge_shards works for the requested Kafka and Pulsar scenarios.

Written by the indexing model from the issue text.