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>

docker/README.md

@@ -27,7 +27,7 @@ The [.env](./.env) file contains important environment variables for Docker.
 - `ES_PORT`  
   The port used to expose the Elasticsearch service to the host machine, allowing **external** access to the service running inside the Docker container.  Defaults to `1200`.
 - `ELASTIC_PASSWORD`  
-  The password for Elasticsearch. When updated, you must revise the `es.password` entry in [service_conf.yaml](./service_conf.yaml) accordingly.
+  The password for Elasticsearch. 
 
 ### Kibana
 
@@ -46,7 +46,7 @@ The [.env](./.env) file contains important environment variables for Docker.
 ### MySQL
 
 - `MYSQL_PASSWORD`  
-  The password for MySQL. When updated, you must revise the `mysql.password` entry in [service_conf.yaml](./service_conf.yaml) accordingly.
+  The password for MySQL. 
 - `MYSQL_PORT`  
   The port used to expose the MySQL service to the host machine, allowing **external** access to the MySQL database running inside the Docker container. Defaults to `5455`.
 
@@ -57,16 +57,16 @@ The [.env](./.env) file contains important environment variables for Docker.
 - `MINIO_PORT`  
   The port used to expose the MinIO API service to the host machine, allowing **external** access to the MinIO object storage service running inside the Docker container. Defaults to `9000`.
 - `MINIO_USER`  
-  The username for MinIO. When updated, you must revise the `minio.user` entry in [service_conf.yaml](./service_conf.yaml) accordingly.
+  The username for MinIO.
 - `MINIO_PASSWORD`  
-  The password for MinIO. When updated, you must revise the `minio.password` entry in [service_conf.yaml](./service_conf.yaml) accordingly.
+  The password for MinIO. 
 
 ### Redis
 
 - `REDIS_PORT`  
   The port used to expose the Redis service to the host machine, allowing **external** access to the Redis service running inside the Docker container. Defaults to `6379`.
 - `REDIS_PASSWORD`  
-  The password for Redis. When updated, you must revise the `redis.password` entry in [service_conf.yaml](./service_conf.yaml) accordingly.
+  The password for Redis.
 
 ### RAGFlow
 
@@ -119,7 +119,7 @@ The [.env](./.env) file contains important environment variables for Docker.
 
 ## 🐋 Service configuration
 
-[service_conf.yaml](./service_conf.yaml) specifies the system-level configuration for RAGFlow and is used by its API server and task executor.
+[service_conf.yaml](./service_conf.yaml) specifies the system-level configuration for RAGFlow and is used by its API server and task executor. In a dockerized setup, this file is automatically created based on the [service_conf.yaml.template](./service_conf.yaml.template) file (replacing all environment variables by their values).
 
 - `ragflow`
   - `host`: The API server's IP address inside the Docker container. Defaults to `0.0.0.0`.
@@ -139,11 +139,11 @@ The [.env](./.env) file contains important environment variables for Docker.
   - `host`: The MinIO serving IP *and* port inside the Docker container. Defaults to `minio:9000`.
 
 - `oauth`  
-  The OAuth configuration for signing up or signing in to RAGFlow using a third-party account.  It is disabled by default. To enable this feature, uncomment the corresponding lines in **service_conf.yaml**.
+  The OAuth configuration for signing up or signing in to RAGFlow using a third-party account.  It is disabled by default. To enable this feature, uncomment the corresponding lines in **service_conf.yaml.template**.
   - `github`: The GitHub authentication settings for your application. Visit the [Github Developer Settings page](https://github.com/settings/developers) to obtain your client_id and secret_key.
 
 - `user_default_llm`  
-  The default LLM to use for a new RAGFlow user. It is disabled by default. To enable this feature, uncomment the corresponding lines in **service_conf.yaml**.  
+  The default LLM to use for a new RAGFlow user. It is disabled by default. To enable this feature, uncomment the corresponding lines in **service_conf.yaml.template**.  
   - `factory`: The LLM supplier. Available options:
     - `"OpenAI"`
     - `"DeepSeek"`