fix(kubestellar): correct container image tags and names in k0s manifests

[castrojo]

Problem

In files/k0s/manifests/kubestellar/:

1. 10-kubeflex-operator.yaml referenced ghcr.io/kubestellar/kubeflex/kubeflex-operator:v0.8.2 which does not exist (the actual GoReleaser / ko image published by kubeflex is ghcr.io/kubestellar/kubeflex/manager:0.8.2).
2. 20-postgres.yaml referenced docker.io/bitnami/postgresql:16.4.0 which returned 404 / NotFound from Docker Hub.
3. 30-kubestellar-core.yaml referenced ghcr.io/kubestellar/kubestellar/controller-manager:v0.25.0 (with leading 'v'), whereas GoReleaser tags the image with SemVer without leading 'v' (0.25.0).

Fix

• Updated 10-kubeflex-operator.yaml to ghcr.io/kubestellar/kubeflex/manager:0.8.2.
• Updated 20-postgres.yaml to standard docker.io/library/postgres:16-alpine.
• Updated 30-kubestellar-core.yaml to ghcr.io/kubestellar/kubestellar/controller-manager:0.25.0.

[castrojo]

Resolved by merged PR #103 (commit 66d5a99).