Provide provisions for 3PA's to persist settings/app data to the API

[asimons04]

Creating this from a thread in the chat.

Basically, there's no way to cover all the possible settings various third-party apps can have via distinct settings columns. Additionally, 3PAs may not currently or even want to poll the server for those and prefer to just have a place to sync their local settings for persistence or to access from another device.

Essentially, provide an authenticated endpoint a user can call that will accept a JSON POST containing the serialized app settings and a companion GET one to retrieve those.

Will leave the specific implementation details to the comments.

[jgrim]

@Pdzly this will be part of the new Sublinks API.

[Pdzly]

I can already sketch it out in the new api #359

[jgrim]

I can already sketch it out in the new api #359

Great!