test: unify e2e utils across e2e/deployment/openshift tests

[GrigoryPervakov]

Why

E2e suites tend to have local helpers that are useful in all of them
This is a preparation step for the later E2E enhancements.

What

Deduplicate and reuse code between different e2e tests suites

[Copilot]

Pull request overview

Centralizes reusable E2E helpers across the E2E, deployment, and OpenShift suites.

Changes:

• Introduces shared environment, readiness, namespace, and read/write helpers.
• Moves diagnostics reporting into a dedicated utility.
• Replaces suite-local implementations with shared helpers.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test/testutil/wait.go	Adds shared readiness and rollout helpers.
test/testutil/utils.go	Adds shared test-namespace helpers.
test/testutil/report.go	Centralizes diagnostic collection.
test/testutil/env.go	Defines shared test environment handles.
test/testutil/checks.go	Centralizes cluster read/write checks.
test/openshift/openshift_test.go	Adopts shared helpers.
test/e2e/keeper_e2e_test.go	Removes duplicated Keeper helpers.
test/e2e/e2e_suite_test.go	Initializes and uses the shared environment.
test/e2e/clickhouse_e2e_test.go	Removes duplicated ClickHouse helpers.
test/deploy/deploy_test.go	Adopts shared deployment and readiness helpers.

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[mintlify]

Docs PR opened: ClickHouse/ClickHouse#116379

Synced the operator's network policies guide and API reference to document new managed NetworkPolicy support for ClickHouse and Keeper clusters.