Allow a self-hosted user to configure their SMTP settings directly from within the UI (#682)

* Add setting fields to model

* Allow to configure SMTP settings

* Normalize locales

* Cleanup locales

* Remove 'coming soon'

* fix test

* Reset credentials

* Reset development config

* Check smtp spelling

* Use post instead of get method

* TLS ENV variable is more descriptive

* Rework application mailer

* Follow rails convention for mailer action params

* Reset schema.rb to main

* Test WIP

* Add test for controller and mailer

* Move tests from controller to model

* Custom error message if settings are not all present

* Comment smtp config in development env

* Add default tls enabled value

* Rubocop

* Fix controller test

* Reset credentials

* Normalize locales

* Test

* fix test

* Fix application mailer test that fails randomly

* Error flash message instead of notice

* Rework application mailer tests

test/models/setting_test.rb

@@ -0,0 +1,23 @@
+require "test_helper"
+
+class AccountTest < ActiveSupport::TestCase
+  test "#send_test_email return true if all smtp settings are populated" do
+    Setting.smtp_host = "smtp.example.com"
+    Setting.smtp_port = 466
+    Setting.smtp_username = "user@example.com"
+    Setting.smtp_password = "notification@example.com"
+    Setting.email_sender = "password"
+
+    assert Setting.smtp_settings_populated?
+  end
+
+  test "#send_test_email return false if one smtp settings is not populated" do
+    Setting.smtp_host = ""
+    Setting.smtp_port = 466
+    Setting.smtp_username = "user@example.com"
+    Setting.smtp_password = "notification@example.com"
+    Setting.email_sender = "password"
+
+    assert_not Setting.smtp_settings_populated?
+  end
+end