✨ Add node offset property

[joao-m-santos]

Closes #314

📝 Description

• Add offset property to AlluvialNode interface
• Calculate node position if offset is valid
• Update documentation and add Storybook example

💥 Is this a breaking change (Yes/No):

• [x] No
• [ ] Yes (please describe the impact and migration path for existing Lume users)

📝 Additional Information

• Missing unit tests

Before submitting the PR, please make sure you do the following

• [x] Read the Contributing Guidelines.
• [x] Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• [x] Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• [x] Ideally, include relevant tests that fail without this PR but pass with it.

[netlify[bot]]

✅ Deploy Preview for adyen-lume ready!

Name	Link
🔨 Latest commit	f70c8c378f942bdddc68f38a62898816b0feab5b
🔍 Latest deploy log	https://app.netlify.com/sites/adyen-lume/deploys/6512f2049ed9b50008805c49
😎 Deploy Preview	https://deploy-preview-315--adyen-lume.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.