Fix concurrency of DerivativeDataSourceManager

- `derivativesRef` shouldn't be static
- Seems that `derivativesRef` shouldn't be atomic; volatile would suffice. This looks like an example of https://github.com/code-review-checklists/java-concurrency#redundant-atomics
- `derivativesRef` doesn't need to store a `ConcurrentHashMap`, a simple `HashMap` would suffice

FYI @zhangxinyu1

Locate DerivativeDataSourceManager and trace every access to derivativesRef, including how instances are created and updated. Verify the requested non-static, volatile reference and simpler map choice against the manager's concurrency behavior, then run the relevant existing Druid tests; done means the requested changes are covered without introducing unsafe concurrent access.

Written by the indexing model from the issue text.