chore(deps): bump langchain in /src/frontend_service

Bumps [langchain](https://github.com/langchain-ai/langchain) from 0.1.20 to 0.3.7.
- [Release notes](https://github.com/langchain-ai/langchain/releases)
- [Commits](langchain-ai/langchain@langchain==0.1.20...langchain==0.3.7)

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

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

src/frontend_service/requirements.txt

@@ -3,7 +3,7 @@ google-cloud-aiplatform==1.53.0
 google-auth==2.29.0
 itsdangerous==2.2.0
 jinja2==3.1.4
-langchain==0.1.20
+langchain==0.3.7
 langchain_google_vertexai==1.0.3
 markdown==3.6
 types-Markdown==3.6.0.20240316