Return structured empty YAML document when no data is available

[onmete]

Description

Currently, mcp server may return an empty string when there are no matching resources for the given arguments. While this is technically a valid outcome, it can make it difficult for downstream consumers (e.g., the LLM) to distinguish between “no results” and an unexpected error or missing data.

Expected Behavior

When there are no results, openshift-mcp should return an empty YAML document that clearly indicates the absence of matching resources while preserving structured output.

Example output with no data