Folders: create a design doc

[VikaCep]

The primary goals of introducing a folders system in Synthetic Monitoring are to:

1. reduce organizational complexity as the number of checks grows and it becomes harder to find and manage them, and

2. enable more granular RBAC, moving beyond today’s coarse, category-level permissions to allow access restrictions at a per-check (or folder) level.

Based on the exploration work done in https://github.com/grafana/synthetic-monitoring/issues/270, the Product DNA doc and the demo meeting we had, we decided that we should move forward with writing a Design Doc to outline the proposed solution, along with their drawbacks and edge cases, to be discussed with the team.

[VikaCep]

Design doc: https://docs.google.com/document/d/1GeLrge15XvQjcj1fS8hKlPfzDePROXSAq9-KIa0rZ0c/edit?tab=t.g93f12lygwz3#heading=h.5sybau7waq2q