Feat : Q CLI should allow a configurable difftool

### Checks

- [x] I have searched [github.com/aws/amazon-q-developer-cli/issues](https://github.com/aws/amazon-q-developer-cli/issues?q=) and there are no duplicates of my issue
- [x] I have run `q doctor` in the affected terminal session
- [x] I have run `q restart` and replicated the issue again

### Operating system

macOS 14.5.0 (23F79)

### Expected behaviour

By splitting screen on VSCode (Code / Editor) - We have an agentic chat for all practical reasons like Cline
Would it be possible to select a difftool as vscode for file updates ?

```
code --diff old.txt new.txt
```

^ would open a side by side panel in VSCode itself

I tried prompting- But the response must be written to a tmp file before doing a diff.

### Actual behaviour

Diffs are only inline

### Steps to reproduce

_No response_

### Environment

```yaml
[q-details]
version = "1.7.1"
hash = "7d766a2d0580db62fae5a4bc2e6eb63946d4d08e"
date = "2025-03-14T22:08:03.470338Z (5d ago)"
variant = "full"

[system-info]
os = "macOS 14.5.0 (23F79)"
chip = "Apple M1 Pro"
total-cores = 10
memory = "32.00 GB"

[environment]
cwd = "/Users/USER"
cli-path = "/Users/USER"
os = "Mac"
shell-path = "/bin/zsh"
shell-version = "5.9"
terminal = "iTerm 2"
install-method = "unknown"

[env-vars]
PATH = "/Users/USER/.codeium/windsurf/bin:/Users/USER/Library/pnpm:/Users/USER/.nvm/versions/node/v20.16.0/bin:/Users/USER/.rbenv/shims:/opt/homebrew/Cellar/node@18/18.20.3/bin:/bin:/usr/bin:/usr/local/bin:/sbin:/opt/homebrew/bin:/opt/homebrew/sbin:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/Applications/Wireshark.app/Contents/MacOS:/Users/USER/.cargo/bin:/Applications/iTerm.app/Contents/Resources/utilities:/Users/USER/.local/bin:/Users/USER/Library/Application Support/Coursier/bin:/Users/USER/.toolbox/bin:/Applications/Visual Studio Code.app/Contents/Resources/app/bin"
QTERM_SESSION_ID = "015047b33e3447eab59b44d028db865a"
Q_SET_PARENT_CHECK = "1"
Q_TERM = "1.7.1"
SHELL = "/bin/zsh"
TERM = "xterm-256color"
__CFBundleIdentifier = "com.googlecode.iterm2"
```