Is your feature request related to a problem?

As we are building extension support for AD, we need to add support for getActions.

getActions enables plugins to register custom transport actions.
With extensions, SDK should be able to support registering transport actions and proxy them to the extension when a transport action is invoked.

• GetActions: OpenSearch to add support for registering Actions #105
• GetActions: Proxy Transport request to an extension #106
• [FEATURE] Add an interface to help HelloWorld extension to register transport action #119