feat: DeeplyReadAgent

[mxdvl]

What does this change?

Note Part of https://github.com/guardian/dotcom-rendering/issues/5554

Reinstate the “Deeply Read“ endpoint at /deeply-read.json.

Does this change need to be reproduced in dotcom-rendering ?

• [ ] No
• [ ] Yes (please indicate your plans for DCR Implementation)

Screenshots

What is the value of this and can you measure success?

Checklist

Does this affect other platforms?

• [ ] AMP
• [ ] Apps
• [ ] Other (please specify)

Does this affect GLabs Paid Content Pages? Should it have support for Paid Content?

• [ ] No
• [ ] Yes (please give details)

Does this change break ad-free?

• [ ] No
• [ ] It did, but tests caught it and I fixed it
• [ ] It did, but there was no test coverage so I added that then fixed it

Does this change update the version of CAPI we're using?

• [ ] No, all the existing database files are just fine
• [ ] Yes, and I have re-run all the tests locally and checked in all the updated data/database/xyz files

Accessibility test checklist

• [ ] Tested with screen reader
• [ ] Navigable with keyboard
• [ ] Colour contrast passed

Tested

• [ ] Locally
• [ ] On CODE (optional)