[Tech Request]: optimize global checkpoint logic

### Is there an existing issue for the same tech request?

- [X] I have checked the existing issues.

### Does this tech request not affect user experience?

- [X] This tech request doesn't affect user experience.

### What would you like to be added ?

```Markdown
created only by incremental checkpoints
1. GC uses it
2. log tail uses it
```

### Why is this needed ?

global checkpoint is needed even though we have the compacted checkpoint. since the global checkpoint may be much smaller than the compacted checkpoint, which contains all `pitr` and `snapshot`

### Additional information

_No response_