Particles - Custom Cache Path

Particles Cache can currently be stored on disk, but it's set to the project's path only (write), which might not suit every artist's need. To address this issue on Linux, a workaround involves creating a symlink that directs to the desired location. However, relying on such workarounds isn't ideal.

I propose to add a box which defaults to the project's path (relative) and that can be modified to input a custom path. The box might be empty by default, and act as custom path only if filled.

Another solution might be to add a toggle which activates the custom path box, like already happens when "[X] External" is checked.