Add tvOS example app instrumented with iOS tracker v2.

The last update of the Demo app with the remote configuration has introduced a bug on the tracker setup.
The screen with the settings has a switch button to choose between "local" and "remote". When it's "local" the app should configure the tracker with the endpoint indicated in the "endpoint" textfield. The last update has broken this feature and the tracker is no longer configured when the switch is on "local".

Update Swift demo apps for remote configuration on tracker v2

Moving here an old tracker issue ticket

The demo app as it stands is very basic in that it is only able to send a flat collection of events with little in the way of user interaction. It would be useful from a testing perspective to:

• Allow the user to change all the currently available settings for the various parts of the tracker
  • Gives us a visual representation of the API and its capabilities
• Define and send custom events in the demo app
  • Custom SelfDescribing Jsons
  • Custom input into our predefined events
• Publish the app to the play store so we have better vision on:
  • Required proguard settings for integrating the Tracker into other apps
  • Much easier for users to download and test the SDK before moving towards integration
  • Much better example of how to use the SDK in an actual application

This would allow us to have a fully defined demo of the SDK which lets users see the full event stream from the Tracker including our new automated events.

Pair of snowplow/snowplow-ios-tracker#652

We want to remove demo apps from snowplow-objc-tracker repository.
The demo apps will be tested along the tracker, downloading the source code from this repository.

The session callback will be introduced with the issue snowplow/snowplow-ios-tracker#664
This issue to add a configuration example in the demo app.

Add demo app that imports the tracker through Swift Package Manager.
It will be used in the tracker CI.