refactor(ci): workflows nested cluster

[universal-itengineer]

Description

Refactors nested-cluster E2E CI workflows and their supporting automation.

The PR replaces large inline workflow shell sections with versioned bash scripts under .github/scripts/bash/e2e, introduces reusable/composite GitHub Actions for repeated setup and artifact tasks, and splits the previous monolithic E2E pipelines into dedicated nightly and release-oriented reusable workflows.

It also adds CI validation for workflow and shell assets with actionlint and shellcheck, plus the static cluster values template and test/e2e CI task entrypoint used by the refactored pipeline.

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

The old nested-cluster E2E workflows mixed orchestration with long inline shell logic, which made the pipeline harder to review, reuse, and lint consistently.

Moving operational steps into tracked scripts and composite actions reduces duplication between nightly and release flows, makes CI behavior easier to maintain, and gives us direct lint coverage for the workflow-related code paths.

What is the expected result?

Nested-cluster nightly and release E2E jobs continue to provision prerequisites, configure storage and virtualization, execute tests, collect encrypted artifacts, and clean up resources through the refactored reusable workflows.

Validation for these changes is available with:

• task lint:shellcheck
• task lint:actionlint
• task e2e:e2e:ci from the repository root
• task e2e:ci inside test/e2e

Checklist

• The code is covered by unit tests. Not applicable: this is CI workflow and scripting refactoring.
• e2e tests passed.
• Documentation updated according to the changes. Composite action README files were added.
• Changes were tested in the Kubernetes cluster manually.

Changelog entries

section: ci
type: chore
summary: "Refactor nested-cluster E2E workflows into reusable pipelines, scripts, and composite actions."
impact_level: low