Add a helper to iterate over all endpoint types in a context store

Unused for now.

Signed-off-by: Ian Campbell <ijc@docker.com>
(cherry picked from commit 4f14c4995e)
Signed-off-by: Silvin Lubecki <silvin.lubecki@docker.com>

cli/context/store/storeconfig.go

@@ -30,6 +30,16 @@ func (c Config) SetEndpoint(name string, getter TypeGetter) {
 	c.endpointTypes[name] = getter
 }
 
+// ForeachEndpointType calls cb on every endpoint type registered with the Config
+func (c Config) ForeachEndpointType(cb func(string, TypeGetter) error) error {
+	for n, ep := range c.endpointTypes {
+		if err := cb(n, ep); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 // NewConfig creates a config object
 func NewConfig(contextType TypeGetter, endpoints ...NamedTypeGetter) Config {
 	res := Config{