feat: update models and add unique viewers endpoint

[ayushtom]

In this PR we do the following things -

• update the models to have a timestamp field
• add a unique page visit endpoint which will add the user's ip address and the page id if it is is his first visit.

For the first task-

• The completed_tasks and achieved collection's models are updated with a required timestamp field of type i64 (we save in unix). We also add these changes to the upsert_completed_task and upsert_completed_achievement since these two functions interact with the collections exclusively.
• I also backfill the old data with timestamp field here https://github.com/starknet-id/upgrade_quest_db/pull/1

For the second task -

• I add a get request on the /unique_page_visit route which accepts a page_id param. The quest pages are identified by some instructions i added in this
• I also check for the followiing things in the logic -
  • if the viewer_ip and viewer_page_id already exist then we don't add it to our collection. The output looks something like this