refactor: PKcols in table, ViewKeyDependency type

* Get PKcols inside tables - done with SQL for tables and
  with an additional step in Haskell for views.

  This fixes an fk column being considered as a pk column on views
  and corrects the test added on
  https://github.com/PostgREST/postgrest/pull/1875/files/1d549768580310e18aac4ffa6dbd01c5b77934a7#r853674126

* classify view key dependencies in SQL

* remove Column from Relationship

* Merge cols/fcols in Relationship and
  ensure allM2ORels and allViewsKeyDependencies fk columns
  are ordered - done by attnum in SQL

* Cardinality now contains relColumns instead of Relationship -
  this simplifies getJoinConditions.

test/spec/Feature/Query/InsertSpec.hs

@@ -595,7 +595,7 @@ spec actualPgVersion = do
             }
 
     context "requesting header only representation" $ do
-      it "returns a location header" $
+      it "returns a location header with a composite PK col" $
         request methodPost "/compound_pk_view" [("Prefer", "return=headers-only")]
             [json|{"k1":1,"k2":"test","extra":2}|]
           `shouldRespondWith`
@@ -606,13 +606,13 @@ spec actualPgVersion = do
                              , "Content-Range" <:> "*/*" ]
             }
 
-      it "should not throw and return location header when a PK is null" $
+      it "returns location header with a single PK col" $
         request methodPost "/test_null_pk_competitors_sponsors" [("Prefer", "return=headers-only")]
             [json|{"id":1}|]
           `shouldRespondWith`
             ""
             { matchStatus  = 201
             , matchHeaders = [ matchHeaderAbsent hContentType
-                             , "Location" <:> "/test_null_pk_competitors_sponsors?id=eq.1&sponsor_id=is.null"
+                             , "Location" <:> "/test_null_pk_competitors_sponsors?id=eq.1"
                              , "Content-Range" <:> "*/*" ]
             }