Allow more targeted runs of eck-diagnostics for large environments

We should consider allowing users to target the diagnostic run to individual resources rather than whole namespaces as the size of the diagnostic archive can get very bit in larger deployments of ECK

The issue names no files, tests, or entry points. Start by locating the eck-diagnostics command that selects namespaces and review how diagnostic archives are assembled. Define the resource-level targeting behavior and verify that a large-environment run collects only the requested resources.

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