Added release notes for v0.15.0 (#4056)

### What problem does this PR solve?



### Type of change


- [x] Documentation Update

docs/release_notes.md

@@ -7,6 +7,40 @@ slug: /release_notes
 
 Key features, improvements and bug fixes in the latest releases.
 
+## v0.15.0
+
+Released on December 18, 2024.
+
+### New features
+
+- Introduces additional Agent-specific APIs.
+- Supports using page rank score to improve retrieval performance when searching across multiple knowledge bases.
+- Offers an iframe in Chat and Agent to facilitate the integration of RAGFlow into your webpage.
+- Adds a Helm chart for deploying RAGFlow on Kubernetes.
+- Supports importing or exporting an agent in JSON format.
+- Supports step run for Agent components/tools.
+- Adds a new UI language: Japanese.
+- Supports resuming GraphRAG and RAPTOR from a failure, enhancing task management resilience.
+- Adds more Mistral models.
+- Adds a dark mode to the UI, allowing users to toggle between light and dark themes.
+
+### Improvements
+
+- Upgrades the document layout recognition model in Deepdoc.
+- Significantly enhances the retrieval performance when using [Infinity](https://github.com/infiniflow/infinity) as document engine.
+
+### Related APIs
+
+#### HTTP APIs
+
+- [List agent sessions](https://ragflow.io/docs/dev/http_api_reference#list-agent-sessions)
+- [List agents](https://ragflow.io/docs/dev/http_api_reference#list-agents)
+
+#### Python APIs
+
+- [List agent sessions](https://ragflow.io/docs/dev/python_api_reference#list-agent-sessions)
+- [List agents](https://ragflow.io/docs/dev/python_api_reference#list-agents)
+
 ## v0.14.1
 
 Released on November 29, 2024.