Document XDCR P2P info message for Neo

MB-49966 introduced a message in the XDCR UI that says (see MB-49966 for an example of the message in the UI):

Performing PeerToPeer communication with the following VBs: [...] 

Since these are info/status messages only, it should be documented so that people are aware. Something like –

Starting in 7.1, you may see a message in the UI XDCR Errors windows like this — “Performing PeerToPeer communication with the following VBs:[…]” — when XDCR is communicating with cluster nodes during replication startup, during cluster topology changes, or in other situations.   The message itself is simply a status/information message and not indicative of an error situation.

A possible place where the message could be documented is here – https://docs.couchbase.com/server/current/manage/manage-xdcr/create-xdcr-replication.html#error-notifications – since that's where the messages will show up. Although the window says "XDCR Errors" – not all of the messages are errors – some are just status or info messages (or possible error messages depending on the scenario).

Background/context (just as an FYI):
The PeerToPeer communication is part of internal XDCR changes to improve XDCR performance during source cluster topology changes (rebalance, failover) by replicating XDCR checkpoint info to all replica nodes in the cluster. This allows XDCR to be incremental on cluster topology change, improving performance.