feat: Support querying sites by facility

[Ikke]

Add support for the facility field to the site datasource so that it can be used to find sites by facility if it's unique, or retrieve the facility for a site.

[fbreckle]

I was wondering if the attribute name should be facility_id, but the description of the attribute is somewhat fuzzy in https://github.com/fbreckle/go-netbox/blob/master/netbox/models/site.go#L72C37-L72C37

	// Local facility ID or description
	// Max Length: 50
	Facility string `json:"facility,omitempty"`

Can this really be ID OR description? 🤔

[Ikke]

Seems like that's incorrect in the netbox documentation. The field is just a string, not a reference to an object (there is no facility entity).

https://demo.netbox.dev/api/dcim/sites/?facility=DSW returns

{
   "id": 22,
   "url": "https://demo.netbox.dev/api/dcim/sites/22/",
   "display": "D. S. Weaver Labs",
   "name": "D. S. Weaver Labs",
   [..],
   "facility": "DSW",
}