Add the new `fqdn` field from the Record model to global search

[peteeckel]

The new field that contains the FQDN of records should be contained in the NetBox global search index, making it possible to search for fully qualified domain names globally.

That was also feature idea by @squintfox in #171 that I originally had the idea of implementing in SQL, but for reasons explained in #231 shied away from - and eventually decided not to follow that path for those reasons.

Now that the fqdn field is in place it is finally possible.