[chore][receiver/k8scluster] Add pods field to allocatable_types_to_report parameter options (open-telemetry#39924)

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Fixes open-telemetry#39923

Signed-off-by: odubajDT <[email protected]>

Author: odubajDT

receiver/k8sclusterreceiver/README.md

@@ -59,6 +59,7 @@ The following allocatable resource types are available.
   - memory
   - ephemeral-storage
   - storage
+  - pods
 - `metrics`: Allows to enable/disable metrics.
 - `resource_attributes`: Allows to enable/disable resource attributes.
 - `namespace`: Allows to observe resources for a particular namespace only. If this option is set to a non-empty string, `Nodes`, `Namespaces` and `ClusterResourceQuotas` will not be observed.