Add inline plugins for the groups

[Gsantomaggio]

So we can mix existing groups with the inline definition.

It is useful to create plugins for specific situations, for example, I want to add the traefik binding for arg-workflow plugin.
so it is:

plugin-type: group
group-name: argo-workflow-binding
plugins:
   - name: argo-workflow  # <<--- here it uses the official plugin
    enabled: true
inline-plugins:
  - plugin-name: Argo-bind-traefik  # <<--- here It defines a plugin only for this specific case.
    yaml:
      - url: "https://raw.githubusercontent.com/kf5i/k3ai-plugins/main/common/traefik/argo-bind.yaml"

Don't merge yet, I'd like to merge #51 before