chore(ci): encrypt test artifacts

[nevermarine]

Description

Encrypt sensitive E2E workflow artifacts before upload and simplify artifact handling for reusable pipeline jobs.

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

The reusable E2E workflow uploads artifacts that may contain sensitive access data such as SSH material, kubeconfig, and failed test dumps. These artifacts should not be stored in plain form in GitHub Actions.

This change adds GPG-based protection for sensitive artifacts while keeping non-sensitive artifacts in plain form to avoid unnecessary complexity. It also updates artifact upload steps to actions/upload-artifact@v7 to support raw uploads without extra archiving.

What is the expected result?

1. Run the reusable E2E workflow.
2. Verify that SSH config, kubeconfig, E2E result bundles, and failed-test resources are uploaded as GPG-encrypted artifacts.
3. Verify that generated files and the final E2E report are uploaded unencrypted.
4. Verify that the report preparation job can download and decrypt encrypted E2E result bundles successfully.

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: chore
summary: "Encrypt sensitive E2E workflow artifacts before upload."
impact_level: low