Write a design doc for "Trusted Workspaces" (for procmacros)

[Arcticae]

An uneasiness appeared in the community about prebuilt procmacros, that CairoLS will now happily execute arbitrary code whenever the user pastes whatever Scarb.toml/Cairo code they get from the internet.

A long-term solution is to sandbox procmacros, but a short-term idea is to write a system that will ask the user to explicitly allow running all proc macros in a workspace/particular procmacros (identifier by PackageId?)/something like this.

Write a design doc, to be shared with #crust.

Important considerations:

1. Investigate whether we can make use of https://code.visualstudio.com/docs/editor/workspace-trust for this mechanism and whether it solves this need.
2. Plan and design UX for non-VSCode editors.
3. Plan what should happen on procmacro updates.