Feat: Adds OpenSearch2.19.1 as the vector_database support (#7140)

### What problem does this PR solve?

This PR adds the support for latest OpenSearch2.19.1 as the store engine
& search engine option for RAGFlow.

### Main Benefit

1. OpenSearch2.19.1 is licensed under the [Apache v2.0 License] which is
much better than Elasticsearch
2. For search, OpenSearch2.19.1 supports full-text
search、vector_search、hybrid_search those are similar with Elasticsearch
on schema
3. For store, OpenSearch2.19.1 stores text、vector those are quite
simliar with Elasticsearch on schema

### Changes

- Support opensearch_python_connetor. I make a lot of adaptions since
the schema and api/method between ES and Opensearch differs in many
ways(especially the knn_search has a significant gap) :
rag/utils/opensearch_coon.py
- Support static config adaptions by changing:
conf/service_conf.yaml、api/settings.py、rag/settings.py
- Supprt some store&search schema changes between OpenSearch and ES:
conf/os_mapping.json
- Support OpenSearch python sdk : pyproject.toml
- Support docker config for OpenSearch2.19.1 :
docker/.env、docker/docker-compose-base.yml、docker/service_conf.yaml.template

### How to use
- I didn't change the priority that ES as the default doc/search engine.
Only if in docker/.env , we set DOC_ENGINE=${DOC_ENGINE:-opensearch}, it
will work.


### Others
Our team tested a lot of docs in our environment by using OpenSearch as
the vector database ,it works very well.
All the conifg for OpenSearch is necessary.

### Type of change

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

---------

Co-authored-by: Yongteng Lei <yongtengrey@outlook.com>
Co-authored-by: writinwaters <93570324+writinwaters@users.noreply.github.com>
Co-authored-by: Yingfeng <yingfeng.zhang@gmail.com>

api/settings.py

@@ -19,6 +19,7 @@ from enum import IntEnum, Enum
 import json
 import rag.utils.es_conn
 import rag.utils.infinity_conn
+import rag.utils.opensearch_coon
 
 import rag.utils
 from rag.nlp import search
@@ -132,11 +133,14 @@ def init_settings():
 
     global DOC_ENGINE, docStoreConn, retrievaler, kg_retrievaler
     DOC_ENGINE = os.environ.get('DOC_ENGINE', "elasticsearch")
+    # DOC_ENGINE = os.environ.get('DOC_ENGINE', "opensearch")
     lower_case_doc_engine = DOC_ENGINE.lower()
     if lower_case_doc_engine == "elasticsearch":
         docStoreConn = rag.utils.es_conn.ESConnection()
     elif lower_case_doc_engine == "infinity":
         docStoreConn = rag.utils.infinity_conn.InfinityConnection()
+    elif lower_case_doc_engine == "opensearch":
+        docStoreConn = rag.utils.opensearch_coon.OSConnection()
     else:
         raise Exception(f"Not supported doc engine: {DOC_ENGINE}")