Allow pull from upstream for non-git upstreams

[lbarcziova]

• [ ] use the implementation from packit/packit#2147 (initialise PackitAPI for pull-from-upstream with non_git_upstream=True if upstream_project_url is None in package config)
• [ ] figure out the DB event handling
  • currently, the ProjectReleaseModel is always used
  • the model is added here
• [ ] if needed, update the API implementation here and here (and the same for dashboard)
• [ ] adjust packit dist-git init to not require the upstream_project_url in config

Part of #2202 epic