Link to the archived wiki page for oauth help

[islemaster]

Update the broken link in our developer OAuth setup help link (only visible in development).

Before	After

We were still linking to our old wiki, which went down years ago. The page in question has been archived here.

Testing story

Tested manually on local machine by signing out and visiting /users/sign_in.

Reviewer Checklist:

• Tests provide adequate coverage
• Code is well-commented
• New features are translatable or updates will not break translations
• Relevant documentation has been added or updated
• User impact is well-understood and desirable
• Pull Request is labeled appropriately
• Follow-up work items (including potential tech debt) are tracked and linked

[maddiedierker]

thank you for updating this!