docs: Add consent banner (#50302)

Adds a consent banner, similar to the one on zed.dev

Before you mark this PR as ready for review, make sure that you have:
- [x] Added a solid test coverage and/or screenshots from doing manual
testing
- [x] Done a self-review taking into account security and performance
aspects
- [x] Aligned any UI changes with the [UI
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)

Release Notes:

- N/A

.github/workflows/deploy_cloudflare.yml

@@ -26,6 +26,7 @@ jobs:
           CC: clang
           CXX: clang++
           DOCS_AMPLITUDE_API_KEY: ${{ secrets.DOCS_AMPLITUDE_API_KEY }}
+          DOCS_CONSENT_IO_INSTANCE: ${{ secrets.DOCS_CONSENT_IO_INSTANCE }}
 
       - name: Deploy Docs
         uses: cloudflare/wrangler-action@da0e0dfe58b7a431659754fdf3f186c529afbe65 # v3