Issue Description

When an unindexed search, or an unindexed search component, is used we log notes=A (for fully unindexed), or notes=U(unindexed filter component) in the access log.

Notes=U is the tricky one because it's not always "bad", but it should be investigated none the less.

One way to help troubleshoot/investigate notes=A/notes=U would be add more info to the message about what attributes in the filter were unindexed (and why? No index or id scan limit exceeded).

The format could be something like:

notes=U[<list of unindexed attributes>]
notes=U[objectclass(missing index), mail(exceeded id scan limit)]

Or even do a dictionary format for easier parsing by external tools:

notes=U{<dict of unindexed attributes>}
notes=U{objectclass: missing index, mail: exceeded id scan limit}

We could also add a new access logging level to trigger this extra info, but if there isn't much overhead to doing it then it should be logged by default (no special log level).