feat: bump llama.cpp, add gguf support

[mudler]

Description

This PR syncs up the llama backend to use gguf (go-skynet/go-llama.cpp#180). It also adds llama-stable to the targets so we can still load ggml. It adapts the current tests to use the llama-backend for ggml and uses a gguf model to run tests on the new backend.

In order to consume the new version of go-llama.cpp, it also bump go to 1.21 (images, pipelines, etc)

[mudler]

let's see how it goes!