Fix: better start experience PYTHONPATH in shell (#5593)

### What problem does this PR solve?

As title export PYTHONPATH in the shell

### Type of change

- [x] Refactoring

Signed-off-by: yihong0618 <zouzou0208@gmail.com>

docker/launch_backend_service.sh

@@ -5,6 +5,7 @@ set -e
 
 # Unset HTTP proxies that might be set by Docker daemon
 export http_proxy=""; export https_proxy=""; export no_proxy=""; export HTTP_PROXY=""; export HTTPS_PROXY=""; export NO_PROXY=""
+export PYTHONPATH=$(pwd)
 
 export LD_LIBRARY_PATH=/usr/lib/x86_64-linux-gnu/
 
@@ -100,4 +101,4 @@ run_server &
 PIDS+=($!)
 
 # Wait for all background processes to finish
-wait
+wait