Replace auto failover 'max events' with 'max nodes'

With the introduction of multi-node auto failover in 7.1, we no longer track auto-failover events and instead count auto-failover nodes.

Wherever the docs say 'events' it should be replaced with 'nodes'. I think the following are some of the pages (there could be more):

• https://docs.couchbase.com/server/current/learn/clusters-and-availability/automatic-failover.html  (probably even the page that I reviewed for Ray Offiah still says events since I did not point it out during the review)
• https://docs.couchbase.com/server/current/rest-api/rest-cluster-autofailover-settings.html
• https://docs.couchbase.com/server/current/rest-api/rest-cluster-autofailover-enable.html