feat: display selectInstance menu post-installation

[SethFalco]

While working on #42, I noticed something that was worth resolving.

The addon defines a default instance in its settings, invidious.snopyta.org. However, there will eventually come a time that someone installs this extension, and their first experience with it is that everything is broken because the instance is down.

Ideally, they'll understand why and know to go to the settings, but we probably shouldn't assume that. It'd be nice to be as friendly as possible to the uninitiated.

The previous Invidious addon I used by TheAssassin had this problem before in TheAssassin/kodi-invidious-plugin@5474b45.

Some addons like JellyCon display a setup process once installed, for example:

Displayed immediately after installation, showing local servers it can find.

I think this extension should do something similar, where after installation, you display the selectInstance menu? You can still keep the default as invidious.snopyta.org in case they close the menu without selecting anything.

The objective being to preserve the initial user-experience when or if invidious.snopyta.org is down, and the default in settings.xml hasn't been updated yet.

[lekma]

not a bad idea...let me think about it