[optimize](load) Update Threshold for Force Flush in Batch Stream Load

[vinlee19]

Proposed changes

The maximum stream load data is limited to 10GB by default in Apache Doris. If the data exceeds the streaming_load_max_mb limit, the task will fail. To prevent this issue, we can set a threshold for the stream load task to force a flush.

Issue Number: close #xxx

Problem Summary:

Describe the overview of changes.

Checklist(Required)

1. Does it affect the original behavior: (Yes/No/I Don't know)
2. Has unit tests been added: (Yes/No/No Need)
3. Has document been added or modified: (Yes/No/No Need)
4. Does it need to update dependencies: (Yes/No)
5. Are there any changes that cannot be rolled back: (Yes/No)

Further comments

If this is a relatively large or complex change, kick off the discussion at [email protected] by explaining why you chose the solution you did and what alternatives you considered, etc...