Doc edits to the App Logs section

In https://docs.couchbase.com/server/5.5/eventing/eventing-debugging-and-diagnosability.html

It says the default location of Application logs. However, we also need to mention where it would go if the paths were customized during cluster setup.

This directory is relative to the "Indexes Path" chosen in UI during setup, please see below:

https://docs.couchbase.com/server/4.1/clustersetup/_images/admin/cluster-setup-01.png

It goes under the chosen "Indexes Path" location into @eventing directory under that.

Update the document to indicate where the Application logs are stored, when non-default paths are used.