[Feature] Execute ManifestFileMeta#merge asynchronously to reduce the time of snapshot commit.

### Search before asking

- [X] I searched in the [issues](https://github.com/apache/incubator-paimon/issues) and found nothing similar.

### Motivation

In the snapshot commit phase, `ManifestFileMeta` will be merged. Consider this situation: when a partition expires, `fullCompaction` will be triggered according to the merge algorithm. At this time, all historical `ManifestEntry` will be rewritten into the new `ManifestFile`, and the time will increase with the number of `ManifestEntry`.

I tested about 20 * 40000 `ManifestEntry` and it took about 5 minutes.

### Solution

I think the merge of `ManifestFileMeta` can also be executed asynchronously like compaction.

### Anything else?

_No response_

### Are you willing to submit a PR?

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