Support Policies

Reposting this for visibility, as I'm not sure anyone will see a comment on a closed issue and I haven't heard anything for a week.

> The upstream issue was resolved, but unfortunately VSCode disables policies (the partial solution to the problem) for VSCode Web. Would it be reasonable to make policies apply to code-server?
>
> https://github.com/microsoft/vscode/issues/27972 is still open, but it would be nice to at least get the policy stuff over to code-server.
>
> While I was trying to hack around this locally my AI coding assistant narrowed down to what it thinks the problem is (and which seems like a reasonable guess), which is that the `ConfigurationService` that is instantiated for the electron app includes a `policyService`
> https://github.com/microsoft/vscode/blob/main/src/vs/code/electron-main/main.ts#L226
> But the configuration service that is instantiated for VSCode Server uses a `NullPolicyService`.
> https://github.com/microsoft/vscode/blob/main/src/vs/server/node/serverServices.ts#L145
>
> Of note, the policy service on Linux is just a JSON file in a particular location, which I think would all that would be needed here.
>
> In theory, the only patch necessary to fix this for code-server would be to change VSCode Server to instantiate a policyService and use it. I suspect that reality is quite different from theory, as always, but this feels like it has potential to be a low-lift improvement.

_Originally posted by @MicahZoltu in [#6995](https://github.com/coder/code-server/issues/6995#issuecomment-3870709116)_