Add a unique "sytem name" to Demux::App

[rreinhardt9]

Sometimes in the parent app, it's important to know something about one of the specific apps.

For example, if you want to show or hide some part of the UI depending on if a specific app has been connected.

Maybe you want to include a banner in an email encouraging them to try a new app but only if they haven't connected it yet.

Another example is if your parent app runs in multiple environments, your Demux::App records for the same "app" might all have different primary keys. If you want to run a data migration that impacts "app X" in all environments, it would be helpful to have a handle to refer to it that you could make the same in each of the environments.

In these cases, it seems like it would help to have a unique and stable way to refer to that specific app besides the primary key.

What if we add a column to Demux::App (maybe called system_name?) that would contain a string uniquely identifying this app ("slack_integration" for example).

It wouldn't really serve any purpose in the Demux library itself; which gives me some pause when adding it. But it would allow the parent app to interface with Demux in more meaningful ways...