Support metadata compaction

### Feature Request / Improvement

Add support for compaction. This rewrites the existing manifests into a single one, reducing the number of calls to the object store. This should follow the Java configuration keys:

- `commit.manifest-merge.enabled`: Controls whether to automatically merge manifests on writes.
- `commit.manifest.min-count-to-merge`: Minimum number of manifests to accumulate before merging.
- `commit.manifest.target-size-bytes`: Target size when merging manifest files.