Unification of the Community Donation and Foundation Donation pages

When you search for "Bevy engine donation" via your favourite search engine, you will see both [Supporting Bevy Development](https://bevyengine.org/community/donate/) and [Donate](https://bevyengine.org/donate/). To me, it's not immediately clear how these are related, especially as the latter is linked at the top-right under "Donate".

The two potential solutions that come to mind are:

- Merge the two pages, with redirects
- Explicitly cross-link the pages and explain the relationship between them

Locate the source pages corresponding to /community/donate/ and /donate/ and read how each is presented and linked. Confirm with maintainers whether the pages should be merged or cross-linked, then update the relevant page sources so the relationship is explicit and verify the resulting links or redirect.

Written by the indexing model from the issue text.