Refactor Retrievers related Examples

[letonghan]

Description

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.

Issues

Fix the Examples CI issues of PR opea-project/GenAIComps#1138.

Type of change

List the type of change like below. Please delete options that are not relevant.

• Others (enhancement, documentation, validation, etc.)

Dependencies

None

Tests

None

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues found.

Scanned Files

[letonghan]

Need to be merged after this pr merged: opea-project/GenAIComps#1138

[chensuyue]

Need to update image build path in test code and test with 1138

[lianhao]

Should this be changed with the new dataprep at the same time? Because I see the new retriever is not compatible with the old dataprep, the default INDEX_NAME and/or COLLECTION_NAME are different for Redis/Milvus between the old and new image respectively, thus files uploaded by old dataprep image can NOT be retrieved by new retriever.

[letonghan]

Should this be changed with the new dataprep at the same time? Because I see the new retriever is not compatible with the old dataprep, the default INDEX_NAME and/or COLLECTION_NAME are different for Redis/Milvus between the old and new image respectively, thus files uploaded by old dataprep image can NOT be retrieved by new retriever.

@lianhao Thanks for your comment.
Yes, the refactor for dataprep component is in this pr, which will also be merged before the v1.2 release.

Also, I've checked the default INDEX_NAME/COLLECTION_NAME for the new version of retrievers and dataprep.
The INDEX_NAME of Redis is rag_redis and the COLLECTION_NAME of Milvus is rag_milvus, which IS consistent between retrievers and dataprep. (commit link here)

Since the retrievers and dataprep components will be refactored together, the old versions will be discarded.
Please let me know if you have further questions!