improve the memory management for executors

[XuHuaiyu]

Feature Request

Is your feature request related to a problem? Please describe:

1. Now, TiDB does in-memory calculations for all the executors except for HashJoin and MergeJoin, this approach brings the risk of OOM. We can use the external storage to improve the memory usage
2. TiDB tracks the memory space usage of a SQL using a relatively complicated way. We may find a better way to track the memory usage of the chunks.

Describe the feature you'd like:

• A better way to track memory for chunks. #14358
• Use the external storage to reduce the memory usage of some executors #14392

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy: