Add associated ResourcePools to Cluster data

**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:
https://github.com/elastic/beats/blob/7b7cd0cb500a871cafa9483afe6f6321492d2fc0/metricbeat/module/vsphere/cluster/data.go#L42

Start with metricbeat/module/vsphere/cluster/data.go around the cluster data definition and compare it with govmomi's resource pool fields. Confirm how the vsphere module currently serializes cluster data, then expose the associated ResourcePools and verify that each cluster reports them for the stated hardware-utilization use case.

Written by the indexing model from the issue text.