Add associated ResourcePools to Cluster data

[GeorgeGkinis]

Describe the enhancement:
We would like to see which resourcepools are associated to each cluster as this is currently not possible.

Describe a specific use case for the enhancement or feature:
Currently there is no way to be able to see the clusters HW utilization/overcommitment from the vsphere module.
To be able to do that we need to know which resourcepool(s) is associated to which cluster.

This is easily feasible as the govmomi library returns the resourcepools associated to each cluster:
https://github.com/vmware/govmomi/blob/c5801225cdacd60743cf8039cb0ca2b171468b98/vim25/mo/mo.go#L113C1-L113C78

Adding (actually not ommitting) this information to the vsphere module seems to be trivial, as it would propably only constitute a couple of line additions to the source code here:

beats/metricbeat/module/vsphere/cluster/data.go

Line 42 in 7b7cd0c

}

[botelastic]

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