docs: using GH Copilot for AI Assist endpoint

[mscolnick]

Fixes #4305

#### GitHub Copilot

You can use your GitHub Copilot for code refactoring or the chat panel. This requires a GitHub Copilot subscription.

1. Download the `gh` CLI from [here](https://cli.github.com/).
2. Create a token with `gh auth token` and copy the token.
3. Add the token to your `marimo.toml` (or configure in the UI settings in the editor).

```toml title="marimo.toml"
[ai.open_ai]
model = "gpt-4o"
api_key = "gho_..."
base_url = "https://api.githubcopilot.com/"
```

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Name	Status	Preview	Comments	Updated (UTC)
marimo-docs	❌ Failed (Inspect)			May 22, 2025 1:42am

[Copilot]

Pull Request Overview

This PR updates the documentation for configuring and using AI completions with marimo by adding a GitHub Copilot section and standardizing the configuration file path references. Key changes include:

• Introducing a dedicated GitHub Copilot section with setup instructions.
• Updating configuration file paths to use $XDG_CONFIG_HOME/marimo/marimo.toml.
• Standardizing UI configuration hints across various guides.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
docs/guides/editor_features/ai_completion.md	Added GitHub Copilot instructions and updated configuration hints.
docs/guides/configuration/index.md	Updated configuration file path to $XDG_CONFIG_HOME/marimo/marimo.toml.
docs/getting_started/quickstart.md	Updated configuration file path to $XDG_CONFIG_HOME/marimo/marimo.toml.

Comments suppressed due to low confidence (1)

docs/guides/configuration/index.md:26

• Ensure that the change in the configuration file path is also documented in the release notes or migration guide to help users transition smoothly.

in a "$XDG_CONFIG_HOME/marimo/marimo.toml" file.

[Copilot]

For clarity and consistency, consider adding a brief note explaining why the alternative UI configuration exists and when it should be used.

[akshayka]

LGTM

[github-actions]

🚀 Development release published. You may be able to view the changes at https://marimo.app?v=0.13.12-dev16