[receiver/vcenter] Adds vSAN metrics for Clusters

[StefanKurek]

Description:
Waiting on #34082 to be merged first.
Adds a set of default disabled vSAN metrics for Clusters.

vcenter.cluster.vsan.throughput          (direction={read/write})
vcenter.cluster.vsan.iops                (direction={read/write})
vcenter.cluster.vsan.latency.avg         (direction={read/write})
vcenter.cluster.vsan.congestions

Link to tracking Issue:
#33556

Testing:
Unit tests added for scraper.
Could not add client tests as govmomi vSAN simulator currently not implemented.
Test against live environment.

Documentation:
New documentation generated