Should publish to ghcr.io by default

### What problem are you facing?

This template currently does not publish to ghcr.io by default, only upbound marketplace (if credentials are supplied).

This goes against [Crossplane Policies](https://github.com/crossplane/crossplane/blob/main/GOVERNANCE.md#policies-for-community-extension-projects) for publications: `Build artifacts, e.g. Crossplane packages (opinionated OCI images), must be published to the crossplane-contrib org on GitHub Container Registry (ghcr.io), which will serve as a neutral community registry.`

### How could Crossplane help solve your problem?

The provider template should be updated to match this requirement