chore(ci): remove encryption from e2e manifests

[nevermarine]

Description

Adjust the reusable E2E workflow artifact handling.

Why do we need it, and what problem does it solve?

The workflow artifact flow became inconsistent after introducing GPG encryption for E2E artifacts. We need predictable upload and download behavior, correct handling for non-archived uploads, and clear operator guidance for encrypted artifacts.

What is the expected result?

1. Generated files, SSH config, and kubeconfig artifacts are uploaded in the intended format.
2. Cleanup downloads and decrypts generated files correctly before undeploy.
3. E2E test results and failed-test manifests are uploaded without encryption.
4. The workflow summary explains how to decrypt encrypted artifacts manually.

Checklist

• The code is covered by unit tests.
• e2e tests passed.
• Documentation updated according to the changes.
• Changes were tested in the Kubernetes cluster manually.

Changelog entries

section: ci
type: fix
summary: "Fix E2E workflow artifact upload and download handling for encrypted generated files."
impact_level: low