[v2.12] add prime mode logic to the provisioning-tests script

[jferrazbr]

Issue #51881

Prepare KDM CI and test scripts to work when KDM marks Prime-only Kubernetes versions. Same idea as PR #1822 for v2.9, adapted per branch.

Problem

KDM CI and test scripts needs to:

• Detect when a selected Kubernetes version requires Prime.
• Choose staging or production Prime registry.
• Fail early with a clear message if Prime is required but no registry endpoint is available in the environment.
• Keep non-Prime behavior unchanged.

Solution

• Prime detection in scripts:

  • Read channels, compare the release item’s "minChannelServerVersion" with "LAST_COMMUNITY_RANCHER" to decide Prime.
  • Pick "staging" or "production" Prime based on the version tag pattern.
  • Set "PRIME_MODE" and "PRIME_REG_HOST" for downstream provisioning test.

• Early guard:

  • If "PRIME_MODE" is 1 but no registry endpoint is present, stop with a user-friendly message that explains why.

• Defaults and safety:

  • Respect an already set "CATTLE_AGENT_IMAGE" from the environment. Only set a default if it is empty.
  • Keep normal flow when Prime is not required.

• Workflow integration:

  • Variables "LAST_COMMUNITY_RANCHER" and "PRIME_AGENT_IMAGE" are passed from the workflow env. Scripts keep safe defaults for local runs.

[jferrazbr]

Green run with prime test from this commit ✔️