Extract operationId from NetworkUpgradeExecute CR in upgrade_monitor

**Epic:** #1080

The `operationId` is stored in the NetworkUpgradeExecute CR spec. Extract it using the existing unstructured accessor pattern and thread it through to `RunPhaseJobs` calls.

```go
operationID, _, err := unstructured.NestedString(cr.Object, "spec", "operationId")
```

## Acceptance Criteria
- [ ] `operationId` extracted correctly from CR
- [ ] Used as the `LabelOperationID` value on launched Jobs
- [ ] Returns error if field is absent or empty

Start in upgrade_monitor at the NetworkUpgradeExecute custom resource handling and trace the existing unstructured accessor pattern through the RunPhaseJobs calls. Verify that missing or empty operationId returns an error and that launched Jobs receive it as LabelOperationID.

Written by the indexing model from the issue text.