Apply Redirection strategy

[LaurenFBaily]

https://www.notion.so/wellcometrust/Url-work-planning-86445fd42f724eb69a55961db7a4dd57

We need to plan when and how we do the redirects.

ID to UID

This can be done whenever as both are currently supported.
We need to determine HOW to do it though.

URL structure changes

The code with the changes will have to be merged before the redirects are applied.
We might want to display a banner on the website during this deployment as some pages will 404 until redirects are applied.

• We need to determine HOW we apply those redirects
• We need to determine WHEN we apply them (@LaurenFBaily to let us know the best date and time)

[rcantin-w]

ID to UID: explore having a helper function on the server side that looks if the URL matches the fetched document's ID. If so, change that part of the URL to be the fetched document's UID.

URL structure changes: For pages. We still have the file /pages/[pageId]. We could add a step (server-side) that gets the fetched document's site section and UID and builds the correct redirection target based on that. It's not ideal as we have to fetched the document twice, but

1. check if we could have a light query that only returns tags and uid.
2. only people that will have bookmarked these pages will cause this fetch to happen, so it shouldn't happen often.

[rcantin-w]

For the "URL structure changes" part I think we've got this under control and are taking it case by case, with more info on each strategy documented in PRs.

For the "ID->UID" bit, as we have an idea for a strategy and have to wait until we're done with all the other changes, I will renaming this ticket "Apply redirection strategy" and move it back to Next. It will serve to track the work done on that bit.