warning when clicking a link to another Lemmy instance

[Die4Ever]

Requirements

• [X] This is a feature request and not a bug report. Otherwise, please create a new bug report instead.
• [X] Please check to see if this request (or a similar one) already exists.
• [X] It's a single feature. Please don't request multiple features in one issue.

Describe the feature you'd like

I've seen this cause quite a bit of confusion, when you click a link taking you to another instance people wonder why they're no longer logged in. Ideally all the links would support remote follow or similar features, but sometimes people put links in their comments or users get lost in other ways. Maybe there should be a dialog box warning that you're leaving the instance? The links could be compared to the list of known Lemmy instances, or maybe other fediverse instances too.

It could also offer to do a search for the clicked URL, which would find posts, comments, users, communities.

Maybe there could also be a warning for clicking Lemmy's native links like the community sidebar links and the buttons.

[Die4Ever]

This could be done entirely in the front end onClick events. Keep the list of known instances in localStorage and only update it once a day or something. And this only needs to be done for logged in users.

[Die4Ever]

I guess this is an easier version of #1048