refactor: test-e2e to use k3s provider

[togashidm]

Description

This PR migrates the local E2E test infrastructure, manifests, controller logic, and supporting scripts from the RKE2 provider to the KThrees (k3s) provider.

changes:

• e2e resources, manifests, and scripts updated to use KThreesControlPlane and KThreesConfig.
• controller supports patching and reconciling k3s-based clusters, with provider-specific file injection for connect-agent manifests.
• RBAC roles and permissions updated for new provider CRDs.
• test utilities and installer scripts are updated to provision and validate k3s components.
• legacy RKE2 files and references removed.
• comments expanded for clarity.

Fixes # (issue)

Any Newly Introduced Dependencies

no

How Has This Been Tested?

make test
make test-e2e
and run test in cluster-tests repo

Checklist:

• I agree to use the APACHE-2.0 license for my code changes
• I have not introduced any 3rd party dependency changes
• I have performed a self-review of my code