ddl: support ADIMN ALTER DDL JOBS grammer to dynamically adjust related reorg parameters

[fzzf678]

Enhancement

v8.3.0 deleted the dynamic adjustment function of tidb_ddl_reorg_worker_cnt and tidb_ddl_reorg_batch_size, but this function is useful in some scenarios:

• During the DDL operation, the business peak period arrives, and the impact of DDL on the cluster needs to be reduced

• When DDL is executed at a certain stage, the resource usage rate suddenly increases, and the resources available for DDL need to be reduced

• During the add index operation, the user observes that the data backfill speed is slow and needs to increase the backfill concurrency so that the DDL can be completed within the expected time

Although these scenario can be circumvented by canceling and then re-executing the DDL, but it reduces usability and affects user experience, so we need to a convenient and easy way to control some parameters during the DDL operation. We can support ADIMN ALTER DDL JOBS ... to achieve this goal.

[fzzf678]

repeat with #57229