Introduce the key encoding version

### Search before asking

- [X] I had searched in the [issues](https://github.com/apache/kvrocks/issues) and found no similar issues.

### Motivation

The current key encoding has some historical legacy issues, and we need to adjust it through some means while ensuring compatibility.

To do this, first we can persist a key encoding version in storage and read it during loading.

### Solution

_No response_

### Are you willing to submit a PR?

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

The issue names no files, tests, or entry points. Start by locating the existing key-encoding and storage-loading paths, then determine how a persisted encoding version should be represented and read while preserving compatibility; done means the version is stored and available during loading.

Written by the indexing model from the issue text.