how to add a new entry in `Edit CMake Cache UI`?

### Brief Issue Summary

When use `CMake` in my project, I want to install both `Debug/Release`. Then, I need to set `CMAKE_DEBUG_POSTFIX=d`. However, I can not set `CMAKE_DEBUG_POSTFIX=d` in `Edit CMake Cache UI`. Hope `CMake` can add this feature.

### CMake Tools Diagnostics

_No response_

### Debug Log

_No response_

### Additional Information

_No response_

Start by locating the Edit CMake Cache UI entry point and how it reads and writes CMake cache entries. Reproduce the inability to add CMAKE_DEBUG_POSTFIX, then verify that a new cache entry can be added and persisted for a CMake project.

Written by the indexing model from the issue text.