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

spec/models/account_spec.rb

@@ -440,13 +440,6 @@ RSpec.describe Account, type: :model do
     end
   end
 
-  describe '.domains' do
-    it 'returns domains' do
-      Fabricate(:account, domain: 'domain')
-      expect(Account.remote.domains).to match_array(['domain'])
-    end
-  end
-
   describe '#statuses_count' do
     subject { Fabricate(:account) }
 
@@ -737,20 +730,6 @@ RSpec.describe Account, type: :model do
       end
     end
 
-    describe 'by_domain_accounts' do
-      it 'returns accounts grouped by domain sorted by accounts' do
-        2.times { Fabricate(:account, domain: 'example.com') }
-        Fabricate(:account, domain: 'example2.com')
-
-        results = Account.where('id > 0').by_domain_accounts
-        expect(results.length).to eq 2
-        expect(results.first.domain).to eq 'example.com'
-        expect(results.first.accounts_count).to eq 2
-        expect(results.last.domain).to eq 'example2.com'
-        expect(results.last.accounts_count).to eq 1
-      end
-    end
-
     describe 'local' do
       it 'returns an array of accounts who do not have a domain' do
         account_1 = Fabricate(:account, domain: nil)