chore(python): update backend sample to consume grpcio from venv (#3961)

Backends can as well depends on grpcio and require different versions from
the ones that are installed in the system.

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

backend/python/common/template/protogen.sh

@@ -0,0 +1,6 @@
+#!/bin/bash
+set -e
+
+source $(dirname $0)/../common/libbackend.sh
+
+python3 -m grpc_tools.protoc -I../.. --python_out=. --grpc_python_out=. backend.proto