phabricator: model: Reference the forge's instance name in model

As phabricator is an "instance" lister (there exists multiple instances of
phabricator in the wild), we need to reference that information.

In effect, this aligns phabricator lister with for example the gitlab one.

Related T1801
Related P434

swh/lister/phabricator/lister.py

@@ -84,7 +84,8 @@ class PhabricatorLister(SWHIndexingHttpLister):
             'html_url': url,
             'origin_url': url,
             'description': None,
-            'origin_type': repo['fields']['vcs']
+            'origin_type': repo['fields']['vcs'],
+            'instance': self.instance,
         }
 
     def get_next_target_from_response(self, response):

swh/lister/phabricator/models.py

@@ -13,3 +13,4 @@ class PhabricatorModel(IndexingModelBase):
 
     uid = Column(String, primary_key=True)
     indexable = Column(Integer, index=True)
+    instance = Column(String, index=True)