Unable to adjust the reorganization parameters of ddl jobs

[fzzf678]

Bug Report

Please answer these questions before submitting your issue. Thanks!

Previously, we could use the global variables tidb_ddl_reorg_worker_cnt and tidb_ddl_reorg_batch_size to adjust concurrency and batch size. However, after #55334, these configurations can no longer be modified dynamically. As a result, certain DDL jobs may take excessive time to complete or consume too many resources, impacting overall business performance. To mitigate these issues, it’s crucial to have control over the configuration of individual DDL jobs to prevent adverse effects on the system as a whole.

1. Minimal reproduce step (Required)

Run a huge reorg job such as add index. I want to speed it up or reduce the impact on the system.

2. What did you expect to see? (Required)

But there is no method to control.

3. What did you see instead (Required)

There are some methods can be used to adjust the ddl.

4. What is your TiDB version? (Required)

master