Add new package bindings option (#169)

Add new package bindings option

This commit adds list of packages for which genqlient should automatically
generate bindings; it's equivalent to adding all the exported types in the
package to `bindings` explicitly. This can be useful when you're both a client
and a server of the same schema and want to share types. We don't recommend
doing things that way, but the feature isn't too invasive and may be useful for
other purposes.

Co-authored-by: Ben Kraft <[email protected]>

generate/generate_test.go

@@ -175,6 +175,11 @@ func TestGenerateWithConfig(t *testing.T) {
 			StructReferences: true,
 			Generated:        "generated-structrefs.go",
 		}},
+		{"PackageBindings", "", nil, &Config{
+			PackageBindings: []*PackageBinding{
+				{Package: "github.com/Khan/genqlient/internal/testutil"},
+			},
+		}},
 		{"NoContext", "", nil, &Config{
 			Generated:   "generated.go",
 			ContextType: "-",