FIX: Rejected emails should not be cleaned up before their logs (#17648)

* FIX: Rejected emails should not be cleaned up before their logs

If we delete the rejected emails before we delete their associated logs
we will receive 404 errors trying to inspect an email message for that
log.

* don't add a blank line

* test for max value as well

* pr cleanup and add migration

* Fix failing test

spec/lib/validators/delete_rejected_email_after_days_spec.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+describe DeleteRejectedEmailAfterDaysValidator do
+
+  it 'is not valid if value is smaller than the value of SiteSetting.delete_email_logs_after_days' do
+    SiteSetting.delete_email_logs_after_days = 90
+
+    expect { SiteSetting.delete_rejected_email_after_days = 89 }.to raise_error(Discourse::InvalidParameters)
+  end
+
+  it "is not valid if value is greater than #{DeleteRejectedEmailAfterDaysValidator::MAX}" do
+    expect { SiteSetting.delete_rejected_email_after_days = DeleteRejectedEmailAfterDaysValidator::MAX + 1 }.to raise_error(Discourse::InvalidParameters)
+  end
+
+end