ci: Add build and publish nightly package workflow

[ppawlowski]

Description

This pull request introduces the "Build and push package" responsible for building and pushing nr-assistant package to node registry tagged as nightly.

Related Issue(s)

https://github.com/FlowFuse/nr-assistant/issues/6

Checklist

• [x] I have read the contribution guidelines
• [ ] Suitable unit/system level tests have been added and they pass
• [ ] Documentation has been updated
  • [ ] Upgrade instructions
  • [ ] Configuration details
  • [ ] Concepts
• [ ] Changes flowforge.yml?
  • [ ] Issue/PR raised on FlowFuse/helm to update ConfigMap Template
  • [ ] Issue/PR raised on FlowFuse/CloudProject to update values for Staging/Production

Labels

• [ ] Includes a DB migration? -> add the area:migration label