Use Lit Context to share config across all addons

[humitos]

• Reference: https://lit.dev/docs/data/context/

[humitos]

I merged #455 into this PR to give it a try, and I was able to re-display a notification by clicking on the "Change URL" button 🎉 . It seems this Lit Context pattern is proving that's going to work for what we want to do 👍🏼 .

There is going to be some updates we will need to do to our addons, tho. Example: I found that this.autoDismissed reactive property won't work immediately because the render() method returns nothing immediately if it was auto dismissed. That particular example might not be an issue, but it's something to consider.