**Description**
This PR syncs up the `llama` backend to use `gguf`
(https://github.com/go-skynet/go-llama.cpp/pull/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)
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Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
