📝 Update our AP guidance to clarify app deployments and responsibilities

[bagg3rs]

User Story

Need to update our guidance here and explain what we do and don't look after.

Value / Purpose

have a page for our users to understand what is in scope of an application being deployed.

Definition of Done

• Documentation has been written / updated

[bagg3rs]

relates to https://github.com/ministryofjustice/data-platform-support/issues/333

[michaeljcollinsuk]

Closing as we have an epic about the new app registration process, that includes updating documentation about the new app registration process, that includes updating documentation