Percona XtraDB Cluster (PXC) install documentation is woefully out of date

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Hi!

This document refers to Percona XtraDB Cluster (PXC) 5.5 which is woefully out of date.

We can skip 5.6/5.7, because technically the only version that matters now is 8.0.

https://galeracluster.com/library/documentation/install-xtradb.html

I advise also reading https://docs.percona.com/percona-xtradb-cluster/8.0/install-index.html for an example of what the modern installation looks like

We might also want to tell people that telemetry is enabled by default, and how to disable it. https://docs.percona.com/percona-xtradb-cluster/8.0/telemetry.html

I don't think anything besides disabling and a link makes sense in the docs.