Popup a dismissible alert if a user is trying to interact with an instance that is blocked with the current one.

[ShadowJonathan]

Currently I see that beehaw.org is defederating with a lot of instances.

That's understandable, but when I tried searching for communities on instances my current server had blocked, I didn't get any feedback, so we should notify the user about that.

In this instance, the community was on lemmy.world, while beehaw.org had blocked that.