Merge branch 'main' into glitch-soc/merge-upstream

Conflicts:
- `README.md`:
  Upstream README has been changed, but we have a completely different one.
  Kept our `README.md`.
- `lib/sanitize_ext/sanitize_config.rb`:
  Upstream added support for more incoming HTML tags (a large subset of what
  glitch-soc accepts).
  Change the code style to match upstream's but otherwise do not change our
  code.
- `spec/lib/sanitize_config_spec.rb`:
  Upstream added support for more incoming HTML tags (a large subset of what
  glitch-soc accepts).
  Kept our version, since the tests are mostly glitch-soc's, except for cases
  which are purposefuly different.

db/migrate/20170920032311_fix_reblogs_in_feeds.rb

@@ -1,6 +1,6 @@
 class FixReblogsInFeeds < ActiveRecord::Migration[5.1]
   def up
-    redis = Redis.current
+    redis = RedisConfiguration.pool.checkout
     fm = FeedManager.instance
 
     # Old scheme:

db/migrate/20200407202420_migrate_unavailable_inboxes.rb

@@ -2,7 +2,8 @@ class MigrateUnavailableInboxes < ActiveRecord::Migration[5.2]
   disable_ddl_transaction!
 
   def up
-    urls = Redis.current.smembers('unavailable_inboxes')
+    redis = RedisConfiguration.pool.checkout
+    urls = redis.smembers('unavailable_inboxes')
 
     hosts = urls.map do |url|
       Addressable::URI.parse(url).normalized_host
@@ -14,7 +15,7 @@ class MigrateUnavailableInboxes < ActiveRecord::Migration[5.2]
       UnavailableDomain.create(domain: host)
     end
 
-    Redis.current.del(*(['unavailable_inboxes'] + Redis.current.keys('exhausted_deliveries:*')))
+    redis.del(*(['unavailable_inboxes'] + redis.keys('exhausted_deliveries:*')))
   end
 
   def down; end