core: Add docs for RunnableConfigurableFields (#19849)
- [x] **docs**: core: Add docs for `RunnableConfigurableFields`
- **Description:** Added incode docs for `RunnableConfigurableFields`
with example
- **Issue:** #18803
- **Dependencies:** NA
- **Twitter handle:** NA
---------
Co-authored-by: Chester Curme <chester.curme@gmail.com>
