fix: add elkjs

[kurokobo]

Summary

Add elkjs for web container.

The changes in this PR made by:

$ cd dify
$ docker run --rm -it -v ${PWD}:/dify --entrypoint sh node:20-alpine3.20
/ # apk add git
/ # cd /dify/web
/dify/web # yarn add elkjs

I confirmed that the build was successful and that the Dify Web UI can be opened normally.

Closes #11400

Screenshots

N/A

Checklist

Important

Please review the checklist below before submitting your pull request.

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods