Rename slo-servicediscovery and cilium-cluster-churn-n1000p50k (#893)

## Rename pipeline files for improved clarity and organization

### Changes:
- **CNI Benchmark**: Renamed
`cilium-cluster-churn-nodes1000-pods50k.yml` → `cluster-churn.yml`
- Removes scale-specific naming (nodes1000-pods50k) for more generic
reusability
  - Simplifies the filename while maintaining clear purpose

- **Large Cluster Benchmark**: Moved `slo-servicediscovery.yml` →
`service-churn.yml`
- Relocated from CNI Benchmark to Large Cluster Benchmark category for
better categorization
- Renamed to `service-churn.yml` for clearer identification of the test
type

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Co-authored-by: Cuong Nguyen <[email protected]>

Author: nguyenluan3017