feat: Implement Rocksdb log storage

[TaskerJang]

This code introduces the implementation of a Raft storage engine using RocksDB for persisting logs, snapshots, and state. The RocksDBStorage struct is designed to handle Raft logs, making it suitable for distributed systems requiring consensus. Key functionalities include:

• Log Storage: The append method is responsible for storing Raft entries (logs) in RocksDB, with the Raft log index used as the key.
• State Management: hard_state and conf_state methods are provided for retrieving and persisting the hard state and configuration state of Raft nodes.
• Snapshot Management: The create_snapshot and apply_snapshot methods handle the creation and application of Raft snapshots, ensuring that the state is persisted in the event of failures or leader changes.
• Compaction: The compact method provides log compaction functionality, removing older log entries no longer needed by the Raft consensus algorithm.
• Entry Retrieval: Methods such as entries, first_index, and last_index allow efficient retrieval of log entries, terms, and indices.
• Testing: A comprehensive set of unit tests is included to validate the functionality of the storage system, including tests for log append, snapshot application, and index retrieval.

Features

• Persistence: Using RocksDB for durable storage of Raft logs, snapshots, and state.
• Compaction: Efficient log compaction to manage storage size.
• Snapshot Management: Full support for creating and applying Raft snapshots.
• Error Handling: Graceful error handling for missing data or unavailable storage.
• Test Coverage: Extensive tests covering core functionalities such as log appending, snapshot handling, and storage compaction.

[cla-assistant]

All committers have signed the CLA.

[jopemachine]

Thanks!