Allow extensions to contribute Group Policy

[sana-ajani]

As we are investigating Group Policy support, another request is for extensions to also add policies. Now there is a PolicyService we can build on top of, extensions can also expose their settings and promote them to policies. We would have to open up our setting contribution to allow declaring some settings as policies and then respecting it.

[vbjay]

@joaomoreno
Priority of this needs to be visited. Enterprises need to be able to set GPO on VsCode AND Visual Studio or what's the point?

Think it should be a shared don't care if vscode or visual studio or other implementation of live share but common gpo to set policy. If I can do this for Visual Studio why not VSCode. https://learn.microsoft.com/en-us/visualstudio/liveshare/use/policies-visual-studio

Here is why https://jsac.jpcert.or.jp/archive/2024/pdf/JSAC2024_2_3_sasada_hazuru_en.pdf