feat: Ability to delete account for administrators (#1874)

## Description

Add account delete option in the user account settings.

Fixes #1555 

## Type of change

- [ ] New feature (non-breaking change which adds functionality)


![image](https://user-images.githubusercontent.com/40784971/110349673-edcc5200-8058-11eb-8ded-a31d15aa0759.png)

![image](https://user-images.githubusercontent.com/40784971/110349778-0c324d80-8059-11eb-9291-abfbffedde5e.png)


## Checklist:

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my own code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

---------

Co-authored-by: Sojan Jose <sojan@pepalo.com>
Co-authored-by: Sojan Jose <sojan.official@gmail.com>
Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

spec/enterprise/models/account_spec.rb

@@ -221,4 +221,53 @@ RSpec.describe Account, type: :model do
       end
     end
   end
+
+  describe 'account deletion' do
+    let(:account) { create(:account) }
+    let(:admin) { create(:user, account: account, role: :administrator) }
+
+    describe '#mark_for_deletion' do
+      it 'sets the marked_for_deletion_at and marked_for_deletion_reason attributes' do
+        expect do
+          account.mark_for_deletion('test_reason')
+        end.to change { account.reload.custom_attributes['marked_for_deletion_at'] }.from(nil).to(be_present)
+           .and change { account.reload.custom_attributes['marked_for_deletion_reason'] }.from(nil).to('test_reason')
+      end
+
+      it 'sends a notification email to admin users' do
+        mailer = double
+        expect(AdministratorNotifications::AccountNotificationMailer).to receive(:with).with(account: account).and_return(mailer)
+        expect(mailer).to receive(:account_deletion).with(account, 'test_reason').and_return(mailer)
+        expect(mailer).to receive(:deliver_later)
+
+        account.mark_for_deletion('test_reason')
+      end
+
+      it 'returns true when successful' do
+        expect(account.mark_for_deletion).to be_truthy
+      end
+    end
+
+    describe '#unmark_for_deletion' do
+      before do
+        account.update!(
+          custom_attributes: {
+            'marked_for_deletion_at' => 7.days.from_now.iso8601,
+            'marked_for_deletion_reason' => 'test_reason'
+          }
+        )
+      end
+
+      it 'removes the marked_for_deletion_at and marked_for_deletion_reason attributes' do
+        expect do
+          account.unmark_for_deletion
+        end.to change { account.reload.custom_attributes['marked_for_deletion_at'] }.from(be_present).to(nil)
+           .and change { account.reload.custom_attributes['marked_for_deletion_reason'] }.from('test_reason').to(nil)
+      end
+
+      it 'returns true when successful' do
+        expect(account.unmark_for_deletion).to be_truthy
+      end
+    end
+  end
 end