Sovereign cloud updates

[Jan Egil Ring (janegilring)]

This pull request updates the Azure policy assignment instructions in the walkthrough documentation to clarify that policy assignments should be scoped only to the individual resource group (e.g., labuser-01) and not to the entire subscription. This prevents unintended impact on other participants in a shared environment.

Clarification of policy assignment scope:

• Updated instructions in solution-01.md to specify that the "Allowed locations" policy should be assigned at the resource group level, not the subscription, to avoid affecting other users.
• Added a note in solution-01.md under the "Not allowed resource types" policy to assign the policy at the resource group scope and not at the subscription.
• Modified solution-03.md to instruct users to set the scope for the "Storage accounts should have the specified minimum TLS version" policy to their resource group only, with an explicit warning not to select the subscription.