DOP-5192: add facets field to updated pages

[seungpark]

Ticket

DOP-5192

Notes

• This change does not functionally change anything. "facet" field is already returned within a a document, if they are read from the documents collection. (example here)
• The updated_documents collection should return the "facets" field after this related change. This route reads from updated_collections and has no "facets" field in the documents.

README updates

• • This PR introduces changes that should be reflected in the README, and I have made those updates.
• • This PR does not introduce changes that should be reflected in the README