Refactor approvals to use new ApprovalController patterns

Refactor our use of approvals to use new ApprovalController patterns such as approval flows.

This will require close collaboration with the confirmation systems team to flesh out their API to support our custom loaders etc.

Start by locating the existing approvals implementation and the new ApprovalController patterns, including approval flows. The confirmation systems team must first define an API that supports custom loaders; done means approvals use the agreed patterns and the API collaboration is complete.

Written by the indexing model from the issue text.