Share custom configuration (locally stored) with Intellij

### Describe the feature or problem you'd like to solve

I don't want to duplicate my custom configuration locally

### Proposed solution

Ideally, I would like to:
* have a unique folder locally where I store all my custom configurations (Skills, Agent, custom instructions, prompts ...).
* This unique folder can be used in CLI and Intellij
* This unique folder can be backed by a git repository (=> no other files than the customization files)

[Intellij Plugin Custom Instructions](https://docs.github.com/en/copilot/how-tos/configure-custom-instructions/add-repository-instructions#manually-creating-a-global-custom-instructions-file):

> macOS: /Users/YOUR-USERNAME/.config/github-copilot/intellij/
> Windows: C:\Users\YOUR-USERNAME\AppData\Local\github-copilot\intellij\

[CLI](https://docs.github.com/en/copilot/how-tos/copilot-cli/customize-copilot/add-custom-instructions#local-instructions)

> $HOME/.copilot/copilot-instructions.md

https://github.com/microsoft/copilot-intellij-feedback/issues/1465 has been created on Plugin side.