Disable extensions using the commandline

## What is your suggestion?

I would like to disable built-in extensions, as they cannot be uninstalled.

something like:

```
code-server --disable-extension
```

## Why do you want this feature?

I usually build a container with code-server in it and preinstall extensions / preconfigure it.
In the latest version the github extension automatically brings AI chat functions and people are of course confused because they will not work

I would like to disable the built-in extension "vscode.github" in my container image build

## Are there any workarounds to get this functionality today?

ClickOps in each instance.

## Are you interested in submitting a PR for this?

i can try