[Feature] Maintain the limited sorted runs in write-only mode

### Search before asking

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

### Motivation

Currently, when we using `write-only` mode with a dedicated compaction job, then the frontend write job's speed are not limited by the compaction job. It may lead to mismatch speed of the whole pipeline. This will lead to much merge read process during query. So, I think a Write-Stall for the multi write job if the sorted runs exceed the `num-sorted-run.stop-trigger` may do good to the whole pipeline.

### Solution

_No response_

### Anything else?

_No response_

### Are you willing to submit a PR?

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

Start by tracing the write-only mode and the handling of sorted runs, then locate where num-sorted-run.stop-trigger is applied. Determine how a write stall should coordinate with a dedicated compaction job and multiple writers; done means writes are limited when sorted runs exceed the configured trigger, preventing unbounded merge-read growth.

Written by the indexing model from the issue text.