Publish Rust API Docs for bdk-ffi

[thunderbiscuit]

I propose we build and publish the Rust API docs website for this library. I have published a test of this on my fork of bdk-ffi. At first glance it might appear silly to do this since we don't have any Rust users and only users at the bindings layer, but let me outline some of the pros I see:

1. The Rust API docs are clean! Since they are generated directly from our code, they do not contain any of the extra uniffi stuff that pollutes the other API docs website and that Mozilla doesn't make private. See the difference between the Rust docs and the Kotlin docs. The Kotlin docs, while easier to read and navigate for Kotlin devs, contains all sorts of "not supposed to use" types that just pollute the docs but that we can't remove easily.
2. For a number of languages, producing API docs is hard and not at the top of the priority list. For example I've been working with 2 React Native teams on their migration from the old bdk-rn to the new 2.2.0 bdk-rn, and they have no access to API docs at all, and must instead rely on IDE hints and autocomplete. Have a ready-to-go website I can share links to would have been great, even if it's not in their native web-wrapping UI they're familiar with.
3. Even for me and maintainers on the team, I think having access to this would be useful. The API has changed so much over time, it can be hard to answer quickly a question from a user who is not on the latest version. Having access to this as a reference would be fantastic.
4. This will force us to clean up our docs! Building the docs locally throws a ton of warnings regarding broken links. It's a bonus that building this will get us to clean the docs a bit.