Bump langchain from 0.1.17 to 0.3.0 in /backend/requirements

Bumps [langchain](https://github.com/langchain-ai/langchain) from 0.1.17 to 0.3.0.
- [Release notes](https://github.com/langchain-ai/langchain/releases)
- [Commits](langchain-ai/langchain@langchain==0.1.17...langchain==0.3.0)

---
updated-dependencies:
- dependency-name: langchain
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

backend/requirements/default.txt

@@ -26,7 +26,7 @@ huggingface-hub==0.20.1
 jira==3.5.1
 jsonref==1.1.0
 trafilatura==1.12.2
-langchain==0.1.17
+langchain==0.3.0
 langchain-core==0.1.50
 langchain-text-splitters==0.0.1
 litellm==1.50.2