feat(llama.cpp): support embeddings endpoints (#2871)

* feat(llama.cpp): add embeddings

Also enable embeddings by default for llama.cpp models

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

* fix(Makefile): prepare llama.cpp sources only once

Otherwise we keep cloning llama.cpp for each of the variants

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

* do not set embeddings to false

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

* docs: add embeddings to the YAML config reference

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

---------

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>