Rename kubevirt_vmi_migration_disk_transfer_rate_bytes metric (#2708)

##### Short description:
The metric kubevirt_vmi_migration_disk_transfer_rate_bytes renamed, this
PR refactoring the old metric name to the new one.

##### More details:

##### What this PR does / why we need it:

##### Which issue(s) this PR fixes:

##### Special notes for reviewer:

##### jira-ticket:
https://issues.redhat.com/browse/CNV-55919


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-->
## Summary by CodeRabbit

* **Tests**
* Updated VM migration observability tests to reference and validate
memory transfer rate measurements (replacing the previous disk transfer
rate target), ensuring metrics reflect memory transfer behavior.

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settings.</sub>
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Author: OhadRevah

tests/observability/metrics/constants.py

@@ -17,7 +17,9 @@
 KUBEVIRT_VMI_STATUS_ADDRESSES = "kubevirt_vmi_status_addresses{{name='{vm_name}'}}"
 KUBEVIRT_VMI_MIGRATION_DATA_PROCESSED_BYTES = "kubevirt_vmi_migration_data_processed_bytes{{name='{vm_name}'}}"
 KUBEVIRT_VMI_MIGRATION_DATA_REMAINING_BYTES = "kubevirt_vmi_migration_data_remaining_bytes{{name='{vm_name}'}}"
-KUBEVIRT_VMI_MIGRATION_DISK_TRANSFER_RATE_BYTES = "kubevirt_vmi_migration_disk_transfer_rate_bytes{{name='{vm_name}'}}"
+KUBEVIRT_VMI_MIGRATION_MEMORY_TRANSFER_RATE_BYTES = (
+    "kubevirt_vmi_migration_memory_transfer_rate_bytes{{name='{vm_name}'}}"
+)
 KUBEVIRT_VMI_MIGRATION_DIRTY_MEMORY_RATE_BYTES = "kubevirt_vmi_migration_dirty_memory_rate_bytes{{name='{vm_name}'}}"
 KUBEVIRT_VM_DISK_ALLOCATED_SIZE_BYTES = "kubevirt_vm_disk_allocated_size_bytes{{name='{vm_name}'}}"
 KUBEVIRT_VMI_MIGRATIONS_IN_SCHEDULING_PHASE = "kubevirt_vmi_migrations_in_scheduling_phase"

tests/observability/metrics/test_migration_metrics.py

@@ -8,7 +8,7 @@
     KUBEVIRT_VMI_MIGRATION_DATA_REMAINING_BYTES,
     KUBEVIRT_VMI_MIGRATION_DATA_TOTAL_BYTES,
     KUBEVIRT_VMI_MIGRATION_DIRTY_MEMORY_RATE_BYTES,
-    KUBEVIRT_VMI_MIGRATION_DISK_TRANSFER_RATE_BYTES,
+    KUBEVIRT_VMI_MIGRATION_MEMORY_TRANSFER_RATE_BYTES,
     KUBEVIRT_VMI_MIGRATIONS_IN_RUNNING_PHASE,
     KUBEVIRT_VMI_MIGRATIONS_IN_SCHEDULING_PHASE,
 )
@@ -69,7 +69,7 @@ class TestKubevirtVmiMigrationMetrics:
                 marks=(pytest.mark.polarion("CNV-11600")),
             ),
             pytest.param(
-                KUBEVIRT_VMI_MIGRATION_DISK_TRANSFER_RATE_BYTES,
+                KUBEVIRT_VMI_MIGRATION_MEMORY_TRANSFER_RATE_BYTES,
                 marks=(pytest.mark.polarion("CNV-11598")),
             ),
             pytest.param(