Replace `Tracker` with `Mooncake` in Bayesian neural networks example

[yebai]

Let's depreciate the support for Tracker (we mention Trackerin various autodiff doc pages) since it is no longer actively maintained and is known to be problematic for some Bijectors.

[penelopeysm]

Also need to mention Mooncake in the main AD page: https://turinglang.org/docs/tutorials/docs-10-using-turing-autodiff/

[yebai]

@willtebbutt can you help look at this so we can close TuringLang/Turing.jl#2356?