Implement EZP-21404: Allow excluding object owner/author from search

JIRA: https://jira.ez.no/browse/EZP-21404

Currently, the owner names of objects indexed by eZFind will be searchable.
For example, searching for 'Administrator' will display a lot of results on a fresh installation with demo content.

This PR adds an .ini setting to make it possible to exclude the owner_name meta field from searches.