Merge Docs and Academy into Developer Hub

[martineckardt]

• Update Fumadocs version in Docs & Academy
• Create a new landing page for the Developer Hub (Docs and Academy landing pages will remain the same for now)
• change metadata elements too, and check if og/search api rotues work properly
• Combine content and check for any issues
• Raise the PR in docs repo
• rename docs repo to developer-hub
• get the new domain pointing to https://developers.avax.network (no other instance of developers page should exist on avax.network)
• make sure other instances of docs and academy have a dummy next app for redirects
• reorg docs

[ashucoder9]

issues so far: quiz component design and buttons need update. organizing docs/academy links when moving between these two needs work.

https://avalanche-docs-olive.vercel.app/