Add public blocks to /about/blocks (#11298)

* Add automatic blocklist display in /about/blocks

Inspired by https://github.com/Gargron/mastodon.social-misc

* Add admin option to set who can see instance blocks

* Normalize locales files

* Rename “Sandbox” to “Silence” for consistency

* Disable /about/blocks when in whitelist mode

* Optionally display rationale for domain blocks

* Only display domain blocks that have user-facing limitations, and order them

* Redesign table of blocked domains to better handle long domain names and rationales

* Change domain blocks ordering now that rationales aren't displayed right away

* Only show explanation for block severities actually in use

* Reword instance block explanations and add disclaimer for public fetch mode

config/settings.yml

@@ -64,6 +64,8 @@ defaults: &defaults
   peers_api_enabled: true
   show_known_fediverse_at_about_page: true
   spam_check_enabled: true
+  show_domain_blocks: 'disabled'
+  show_domain_blocks_rationale: 'disabled'
 
 development:
   <<: *defaults