API/GetColumns: fix foreign keys being considered pkeys (#2213)

Foreign keys that were unique columns and not pkeys had their column
exclusion disabled in the UI as the current query to fetch column data
was counting them as primary keys. This PR fixes this

### QA

```sql
-- Create a projects table
CREATE TABLE projects (
    id SERIAL PRIMARY KEY, 
    application_id INT
);

-- Create the applications table
CREATE TABLE applications (
    id INTEGER UNIQUE
);

-- Create foreign key relationship
ALTER TABLE projects
ADD CONSTRAINT fk_application
FOREIGN KEY (application_id)
REFERENCES applications (id);
```

Before checking out to this PR, id in the applications table will be
disabled in UI, post checkout - will be non-disabled

flow/cmd/peer_data.go

@@ -297,19 +297,20 @@ func (h *FlowRequestHandler) GetColumns(
 	defer peerConn.Close(ctx)
 
 	rows, err := peerConn.Query(ctx, `SELECT
-		distinct attname AS column_name,
-		format_type(atttypid, atttypmod) AS data_type,
-		(attnum = ANY(conkey)) AS is_primary_key
+    DISTINCT attname AS column_name,
+    format_type(atttypid, atttypmod) AS data_type,
+    (pg_constraint.contype = 'p') AS is_primary_key
 	FROM pg_attribute
 	JOIN pg_class ON pg_attribute.attrelid = pg_class.oid
-	JOIN pg_namespace on pg_class.relnamespace = pg_namespace.oid
+	JOIN pg_namespace ON pg_class.relnamespace = pg_namespace.oid
 	LEFT JOIN pg_constraint ON pg_attribute.attrelid = pg_constraint.conrelid
 		AND pg_attribute.attnum = ANY(pg_constraint.conkey)
+		AND pg_constraint.contype = 'p'
 	WHERE pg_namespace.nspname = $1
 		AND relname = $2
 		AND pg_attribute.attnum > 0
 		AND NOT attisdropped
-	ORDER BY column_name`, req.SchemaName, req.TableName)
+	ORDER BY column_name;`, req.SchemaName, req.TableName)
 	if err != nil {
 		return nil, err
 	}