Integrate k8s 1.28.8

Closes #1107 (closed)

This:

• moves images from K8s versions v1.25|v1.26|v1.27 to v1.26|v1.27|v1.28, the v1.28 built from sylva-projects/sylva-elements/diskimage-builder!177 (merged) evolution;

• adds new entry to units.calico-crd.helm_chart_versions & units.calico.helm_chart_versions, per https://github.com/rancher/rke2/releases/tag/v1.28.8%2Brke2r1:

      v3.25.001: '{{ include "k8s-version-match" (tuple . "<1.26") }}'
      v3.26.101: '{{ include "k8s-version-match" (tuple . ">=1.26.6,<=1.27.6") }}'
      v3.26.300: '{{ include "k8s-version-match" (tuple . ">=1.27.10,<1.28.8") }}'
      v3.27.200: '{{ include "k8s-version-match" (tuple . ">=1.28.8") }}'

(rke2-ingress-nginx chart version 4.8.200 is still used in v1.28.8+rke2r1, per https://github.com/rancher/rke2/releases/tag/v1.28.8%2Brke2r1, hence no units.ingress-nginx.helm_chart_versions addition)

• plus some small cleanup in environment-values/ci/k8s-*1.2*.yml files