Print selective deployment error to container stdio

[kate-goldenring]

We currently do not have a way to surface runwasi errors to K8s events. They are only being surfaced in containerd logs which are not intuitive to search. Just as we print trigger information on startup, it makes sense to print error reasons for the time being to make them easier to discover. Take an app with components hello and goodbye. If i selectively deploy component foo, I will now see the following log in the container log:

Error with selective deployment: Specified component "foo" not found in application

Example SpinApp:

apiVersion: core.spinkube.dev/v1alpha1
kind: SpinApp
metadata:
  name: hello-salutation-spinap-foop
spec:
  # TODO: change to image hosted at ghcr.io/spinkube/spin-operator/salutations when published
  image: "ghcr.io/kate-goldenring/spin-operator/examples/spin-salutations:20241022-144454"
  replicas: 1
  executor: containerd-shim-spin
  components: ["foo"]

ref #228

[radu-matei]

Given there is no easy way for a user to learn about this kind of issue (since we can't do k8s events), this seems a more than reasonable approach.

LGTM

[devigned]

For expedience sake, lgtm, but I'd like to see us provide a more precise way of logging messages to either pod or containerd log. Relying on println and stdout to be the right log destination concerns me.

[Mossaka]

I agree this might be the best we can do right now but I'd like to see a comment in line 149 saying why we are relying on println.

[jsturtevant]

+1 to everyone's comments. I believe this has to do with the way (and timing) of how we fork the container. There is some other discussion in runwasi to revisit the approach which may help.