Refactor Retrievers related Examples (#1387)

Delete redundant retrievers docker image in docker_images_list.md.
Refactor Retrievers related Examples READMEs.
Change all of the comps/retrievers/xxx/xxx/Dockerfile path into comps/retrievers/src/Dockerfile.

Fix the Examples CI issues of PR opea-project/GenAIComps#1138.
Signed-off-by: letonghan <letong.han@intel.com>

ChatQnA/docker_compose/nvidia/gpu/README.md

@@ -104,7 +104,7 @@ cd GenAIComps
 ### 2. Build Retriever Image
 
 ```bash
-docker build --no-cache -t opea/retriever-redis:latest --build-arg https_proxy=$https_proxy --build-arg http_proxy=$http_proxy -f comps/retrievers/redis/langchain/Dockerfile .
+docker build --no-cache -t opea/retriever:latest --build-arg https_proxy=$https_proxy --build-arg http_proxy=$http_proxy -f comps/retrievers/src/Dockerfile .
 ```
 
 ### 3. Build Dataprep Image
@@ -153,7 +153,7 @@ docker build -t opea/nginx:latest --build-arg https_proxy=$https_proxy --build-a
 
 Then run the command `docker images`, you will have the following 5 Docker Images:
 
-1. `opea/retriever-redis:latest`
+1. `opea/retriever:latest`
 2. `opea/dataprep-redis:latest`
 3. `opea/chatqna:latest`
 4. `opea/chatqna-ui:latest` or `opea/chatqna-react-ui:latest`

ChatQnA/docker_compose/nvidia/gpu/compose.yaml

@@ -40,7 +40,7 @@ services:
       https_proxy: ${https_proxy}
     command: --model-id ${EMBEDDING_MODEL_ID} --auto-truncate
   retriever:
-    image: ${REGISTRY:-opea}/retriever-redis:${TAG:-latest}
+    image: ${REGISTRY:-opea}/retriever:${TAG:-latest}
     container_name: retriever-redis-server
     depends_on:
       - redis-vector-db
@@ -55,6 +55,8 @@ services:
       REDIS_HOST: redis-vector-db
       INDEX_NAME: ${INDEX_NAME}
       TEI_EMBEDDING_ENDPOINT: ${TEI_EMBEDDING_ENDPOINT}
+      LOGFLAG: ${LOGFLAG}
+      RETRIEVER_COMPONENT_NAME: "OPEA_RETRIEVER_REDIS"
     restart: unless-stopped
   tei-reranking-service:
     image: ghcr.io/huggingface/text-embeddings-inference:1.5