The Web Components Config API should store config by appId

[willmcvay]

Background context or User story:

See: #1033 and #1289

Currently the web components config API stores config by customerId as it's primary key. This works fine however, it should be expanded so that it can have a secondary key that fetches by an appId - this will allow a customer to have multiple components and a config per app

Specification or Acceptance Criteria:

• Should allow GET, POST, PUT, DELETE endpoints to access config for only the app they need to perform a CRUD operation on.
• Should preserve the existing config, just adding an additional appId layer to the document eg

{
  someCustomerId: {
    someAppId: {
      config: {}
    },
    anotherAppId: {
      config: {}
    }
  }
}