[WIP] feat: Enable ROSA cluster support in HCP backup/restore tests

[mgencur]

This PRs builds on top of #1921 and adds one more commit with the changes described below. Please review that PR first and then the last commit from the current PR. When pull/1921 is merged the current PR needs to be rebased.

• Add external-rosa mode for HC_BACKUP_RESTORE_MODE to support existing ROSA clusters
• Introduce HC_NAMESPACE parameter for configurable cluster namespace management
• Add service cluster kubeconfig support via SC_KUBECONFIG parameter for ROSA ManifestWork operations
• Implement ManifestWork backup/deletion functionality for ROSA cluster lifecycle management
• Add open-cluster-management.io/api dependency to support ManifestWork operations
• Create separate OADP deployment operations for default vs ROSA scenarios
• Skip DPA HCP plugin modification for ROSA where DPA is managed via ManifestWork
• Add VSL_AWS_PROFILE parameter for volume snapshot location AWS profile configuration
• Refactor backup/restore suite to use pluggable deployment strategies
• Update test configuration to handle both regular HCP and ROSA cluster workflows

Why the changes were made

• This is important for testing OADP hypershift plugin in ROSA and for testing bug fixes such as OCPBUGS-56430. So far it was a manual process, but this PR extends the test suite so that the whole procedure can be run automatically.

How to test the changes made

• Steps are described in TESTING.md where a new section was added for HCP/ROSA.

[openshift-ci]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: mgencur
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[openshift-ci]

@mgencur: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/4.20-e2e-test-hcp-aws	d8296b4	link	false	/test 4.20-e2e-test-hcp-aws
ci/prow/unit-test	d8296b4	link	true	/test unit-test

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