Frontend <=> DCR API And Model Overhaul

We'd like to run this as a project within the WebX team at some point.

## Description

### Current Situation

TODO: Add summary of how the JSON frontend <-> DCR API currently works.

### Proposal

TODO: summary to be written up further:

- Thrift API models, similar to https://github.com/guardian/apps-rendering-api-models
- CAPI models directly in DCR
- Internal DCR data model parsed from these models

## Benefits

TODO: to be written up further:

1. Prevents bugs with updates required/optional properties - 500 error
2. Benefit 2

## Work So Far

- The frontend PR: https://github.com/guardian/frontend/pull/25843
- The DCR PR: #7007