Add publish draft button in staging page

[taoerman]

Summary

Added a "Publish draft" button on the staging tree frontend view next to deploy.

Screenshots:

Locally tested the button, and verified "-next.sqlite3" was created from the change event and stored in Minio.

References

https://github.com/learningequality/studio/issues/4471

Reviewer guidance

To test the changes:

• Use ricecooker to create a staging channel
• Test the buttons
• Verify change applied in celery logs
• Check Minio storage for created "-next.sqlite3"