Per-user URL Blocklist

[kevincox]

Requirements

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• Did you check to see if this issue already exists?
• Is this only a feature request? Do not put multiple feature requests in one issue.
• Is this a backend issue? Use the lemmy-ui repo for UI / frontend issues.
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Is your proposal related to a problem?

When browsing Lemmy I also see posts for sites that I don't want to use. Maybe they have too much tracking, or don't work properly or I just want to avoid.

Describe the solution you'd like.

The user can configure a domain or URL pattern blocklist. In the vast majority of views posts that point to matching URLs would not appear.

Describe alternatives you've considered.

Client-side filtering can hide these but results and smaller pages and other oddities like counts not matching up.

Additional context

Similar to #4514, but configurable by the user.