XDCR - Advanced Filtering for deletions

MB-46359 was filed when a document deletion passed through XDCR's advanced filtering. The design for advanced filtering was meant to pass deletions through regardless of the filter expression. However, this design decision was not communicated to the doc team and thus was not officially documented.

1. 

Since this behavior could be detrimental and could cause data-loss if the users are not careful and aware, we should ensure that this system behavior is documented under the XDCR Advanced Filtering section.

2.

(Regarding https://issues.couchbase.com/browse/MB-46359?focusedCommentId=502984&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-502984)

In additional to just defining how the system work, we should see if it is possible to translate MB-46359's description as an example of what could happen what could lead to a data-loss situation (i.e. when editing or removing/adding a replication and thinking that deletes are protected).

We may even mention the "Do not replicate delete" feature as a way to allow this use case to work without replicating delete and thus causing data loss.