Docs: Added a guide on switching document engine (#7692)

### What problem does this PR solve?

### Type of change

- [x] Documentation Update

docs/develop/acquire_ragflow_api_key.md

 ---
-sidebar_position: 3
+sidebar_position: 4
 slug: /acquire_ragflow_api_key
 ---
 

docs/develop/mcp/_category_.json

 {
   "label": "MCP",
-  "position": 4,
+  "position": 40,
   "link": {
     "type": "generated-index",
     "description": "Guides and references on accessing RAGFlow's knowledge bases via MCP."

docs/develop/switch_doc_engine.md

+---
+sidebar_position: 3
+slug: /switch_doc_engine
+---
+
+# Switch document engine
+
+Switch your doc engine from Elasticsearch to Infinity.
+
+---
+
+RAGFlow uses Elasticsearch by default for storing full text and vectors. To switch to [Infinity](https://github.com/infiniflow/infinity/), follow these steps:
+
+:::danger WARNING
+Switching to Infinity on a Linux/arm64 machine is not yet officially supported.
+:::
+
+1. Stop all running containers:
+
+   ```bash
+   $ docker compose -f docker/docker-compose.yml down -v
+   ```
+
+:::cautiion WARNING
+`-v` will delete the docker container volumes, and the existing data will be cleared.
+:::
+
+2. Set `DOC_ENGINE` in **docker/.env** to `infinity`.
+
+3. Start the containers:
+
+   ```bash
+   $ docker compose -f docker-compose.yml up -d
+   ```

docs/guides/team/join_or_leave_team.md

 ---
-sidebar_position: 2
+sidebar_position: 3
 slug: /join_or_leave_team
 ---
 

docs/guides/team/manage_team_members.md

 ---
-sidebar_position: 1
+sidebar_position: 2
 slug: /manage_team_members
 ---
 

docs/guides/team/share_agents.md

 ---
-sidebar_position: 5
+sidebar_position: 6
 slug: /share_agent
 ---
 

docs/guides/team/share_chat_assistant.md

 ---
-sidebar_position: 4
+sidebar_position: 5
 slug: /share_chat_assistant
 ---
 

docs/guides/team/share_knowledge_bases.md

 ---
-sidebar_position: 3
+sidebar_position: 4
 slug: /share_datasets
 ---
 

docs/guides/team/share_model.md

 ---
-sidebar_position: 6
+sidebar_position: 7
 slug: /share_model
 ---