Add default ownership directives to overall omfile module config

When switching over to using the new config directives I found it a bit heavyweight to set file/dir owners per output file.

This allows you to set the default values for the following
- dirOwner
- dirOwnerNum
- dirGroup
- dirGroupNum
- fileOwner
- fileOwnerNum
- fileGroup
- fileGroupNum

Example:

    module(load="builtin:omfile" dirOwner="syslog")