Fix performance on instances list in admin UI (#15282)

- Reduce duplicate queries
- Remove n+1 queries
- Add accounts count to detailed view
- Add separate action log entry for updating existing domain blocks

app/views/admin/instances/index.html.haml

@@ -32,32 +32,10 @@
 
 %hr.spacer/
 
-- @instances.each do |instance|
-  .directory__tag
-    = link_to admin_instance_path(instance) do
-      %h4
-        = instance.domain
-        %small
-          - if instance.domain_block
-            - first_item = true
-            - if !instance.domain_block.noop?
-              = t("admin.domain_blocks.severity.#{instance.domain_block.severity}")
-              - first_item = false
-            - unless instance.domain_block.suspend?
-              - if instance.domain_block.reject_media?
-                - unless first_item
-                  •
-                = t('admin.domain_blocks.rejecting_media')
-                - first_item = false
-              - if instance.domain_block.reject_reports?
-                - unless first_item
-                  •
-                = t('admin.domain_blocks.rejecting_reports')
-          - elsif whitelist_mode?
-            = t('admin.accounts.whitelisted')
-          - else
-            = t('admin.accounts.no_limits_imposed')
-      - if instance.countable?
-        .trends__item__current{ title: t('admin.instances.known_accounts', count: instance.accounts_count) }= number_to_human instance.accounts_count, strip_insignificant_zeros: true
+- if @instances.empty?
+  %div.muted-hint.center-text
+    = t 'admin.instances.empty'
+- else
+  = render @instances
 
-= paginate paginated_instances
+= paginate @instances