feat: 支持强制使用 AUTH LOGIN 以解决 outlook 等邮箱的发件问题 (#4112)

* feat: 支持强制使用 AUTH LOGIN 以解决 outlook 等邮箱的发件问题

* fix: 修复通过 SSL 发送邮件时绕过 AUTH LOGIN 的问题

* fix: remove redundant branch, delete test file, add i18n translations

- Remove redundant else-if branch in SendEmail since auth is already
  computed via getSMTPAuth()
- Delete option_smtp_auth_test.go as requested
- Add i18n translations for '强制使用 AUTH LOGIN' checkbox

common/constants.go

@@ -80,6 +80,7 @@ var InsecureTLSConfig = &tls.Config{InsecureSkipVerify: true}
 var SMTPServer = ""
 var SMTPPort = 587
 var SMTPSSLEnabled = false
+var SMTPForceAuthLogin = false
 var SMTPAccount = ""
 var SMTPFrom = ""
 var SMTPToken = ""