Remove `package-info.json` from template, use `metadata.yaml`

[akeller]

Feature description

package-info.json appears to be the old way to provide info on plugins and plugin groups. In some cases, including this template, plugins have both package-info.json and metadata.yaml where package-info.json is used as a fallback. If both files exist, the info in package-info.json appears to be ignored.

For simplicity, we should remove package-info.json and make sure every plugin created from this tempalte has the "new" metadata.yaml approach.

Related to kestra-io/kestra#14295.