[INTEG-3263] fix: use the html endpoint since json endpoint requires oauth for google drive api

[ryunsong-contentful]

Purpose

• First clean up frontend to have a simple CT button + Google URL Input and then a button to trigger the entry creation
• Update the backend to grab the html to send to the Document agent (this is because google drive json required oauth even for public url docs)
• Everything works until the point where the AI Agent actually processes the doc (this will happen in a follow up)