Add domain search/filter to the "Federation" (/admin/instances) page (#10071)

app/models/domain_block.rb

@@ -24,6 +24,8 @@ class DomainBlock < ApplicationRecord
   has_many :accounts, foreign_key: :domain, primary_key: :domain
   delegate :count, to: :accounts, prefix: true
 
+  scope :matches_domain, ->(value) { where(arel_table[:domain].matches("%#{value}%")) }
+
   def self.blocked?(domain)
     where(domain: domain, severity: :suspend).exists?
   end

app/models/instance_filter.rb

@@ -9,9 +9,13 @@ class InstanceFilter
 
   def results
     if params[:limited].present?
-      DomainBlock.order(id: :desc)
+      scope = DomainBlock
+      scope = scope.matches_domain(params[:by_domain]) if params[:by_domain].present?
+      scope.order(id: :desc)
     else
-      Account.remote.by_domain_accounts
+      scope = Account.remote
+      scope = scope.matches_domain(params[:by_domain]) if params[:by_domain].present?
+      scope.by_domain_accounts
     end
   end
 end