RJS-2788: Update base url in `realm-web`

[kraenhansen]

What, How & Why?

This closes #6585.

☑️ ToDos

• [x] 📝 Changelog entry
• [ ] 📝 Compatibility label is updated or copied from previous entry
• [ ] 📝 Update COMPATIBILITY.md
• [ ] 🚦 Tests
• [ ] 📦 Updated internal package version in consuming package.jsons (if updating internal packages)
• [ ] 📱 Check the React Native/other sample apps work if necessary
• [x] 💥 Breaking label has been applied or is not necessary