Dynamically create the service_conf.yaml file by replacing environment variables from .env (#3341)

### What problem does this PR solve?

This pull request implements the feature mentioned in #3322. 

Instead of manually having to edit the `service_conf.yaml` file when
changes have been made to `.env` and mapping it into the docker
container at runtime, a template file is used and the values replaced by
the environment variables from the `.env` file when the container is
started.
 

### Type of change

- [X] New Feature (non-breaking change which adds functionality)

---------

Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>
Co-authored-by: Zhichang Yu <yuzhichang@gmail.com>

Dockerfile.slim

@@ -122,6 +122,7 @@ ENV PATH="${VIRTUAL_ENV}/bin:${PATH}"
 
 ENV PYTHONPATH=/ragflow/
 
+COPY docker/service_conf.yaml.template ./conf/service_conf.yaml.template
 COPY docker/entrypoint.sh ./entrypoint.sh
 RUN chmod +x ./entrypoint.sh