Fixes the bug 1196 (#1232)

* Current state of the branch.

* Now gRPC is build only when the BUILD_GRPC_FOR_BACKEND_LLAMA variable is defined.

* Now the local compilation of gRPC is executed on BUILD_GRPC_FOR_BACKEND_LLAMA.

* Revised the Makefile.

* Removed replace directives in go.mod.

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Signed-off-by: Diego <38375572+diego-minguzzi@users.noreply.github.com>
Co-authored-by: lunamidori5 <118759930+lunamidori5@users.noreply.github.com>
Co-authored-by: Ettore Di Giacinto <mudler@users.noreply.github.com>