Introduce new fields 'delete_table' and 'delete_partition' in UpdateMetadata RPC

### Search before asking

- [x] I searched in the [issues](https://github.com/alibaba/fluss/issues) and found nothing similar.

### Motivation

In pr #890, we will use TableMetadata#TABLE_DURATION_DELETE_PATH or TableMetadata#TABLE_DURATION_DELETE_ID to represent a table that needs to be deleted, and use PartitionMetadata#PARTITION_DURATION_DELETE_NAME or PartitionMetadata#PARTITION_DURATION_DELETE_ID a partition that needs to be deleted. Although this approach works, but it is difficult to understand. New fields 'delete_table' and 'delete_partition' can be introduced to represent it, but backward compatibility needs to be considered

### Solution

_No response_

### Anything else?

_No response_

### Willingness to contribute

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