[MM-17797] Add Timeout To SMTP Connection (#13251)

* model/config: add timeout setting to email settings

* services/mailservice: add timeout to connection

* app/server_app_adapter: show SMTP connection errors on log

* services/mailservice: add r/w deadline to smtp conn

* services/mailservice: add context timeout

Co-authored-by: mattermod <mattermod@users.noreply.github.com>

model/config.go

@@ -1245,6 +1245,7 @@ type EmailSettings struct {
 	SMTPPassword                      *string `restricted:"true"`
 	SMTPServer                        *string `restricted:"true"`
 	SMTPPort                          *string `restricted:"true"`
+	SMTPServerTimeout                 *int
 	ConnectionSecurity                *string `restricted:"true"`
 	SendPushNotifications             *bool
 	PushNotificationServer            *string
@@ -1325,6 +1326,10 @@ func (s *EmailSettings) SetDefaults(isUpdate bool) {
 		s.SMTPPort = NewString("10025")
 	}
 
+	if s.SMTPServerTimeout == nil || *s.SMTPServerTimeout == 0 {
+		s.SMTPServerTimeout = NewInt(10)
+	}
+
 	if s.ConnectionSecurity == nil || *s.ConnectionSecurity == CONN_SECURITY_PLAIN {
 		s.ConnectionSecurity = NewString(CONN_SECURITY_NONE)
 	}