CiviConnect - Allow services to define a welcome dialog

In the metadata.json for each CiviConnect app, allow the links to enable the option welcome. If enabled, the UI will automatically open the welcome link after connecting. This is useful for displaying important settings, "next steps", or other docs.

Note: This is only a "Welcome" screen and is not a mandatory screen. Users may or may not pay attention to forms/options/suggestions on the welcome screen. Moreover, if you write a headless script to connect multiple services, then there would be no opportunity to display the "Welcome" screen. Never-the-less, the "Welcome" screen should still be quite helpful in ordinary usage.