[ALOY-419] Create "alloy generate adapter" command

Create a command, template, and instructions for creating custom sync adapters via the alloy CLI. We will also need to make a special directory in alloy projects for creating and maintaining custom adapters. Currently developers are putting them in *app/assets/alloy/sync*, but a more specific location in the project would likely make more sense.

alloy generate adapter NAME

The above command would create a template adapter with the name *NAME*. The template adapter should behave as the no-sync adapter does (ALOY-404), being fully operational, but having no built in persistence. This will ensure that adapters are at least initially setup in a way that is in line with the existing adapters and works with model-view binding. The developer would be left to fill in the persistence sync aspect.