Change resend to using smtp

Signed-off-by: Asai Neko <sugar@sne.moe>

config/types.go

@@ -40,8 +40,13 @@ type search struct {
 }
 
 type email struct {
-	ResendApiKey string `yaml:"resend_api_key"`
-	From         string `yaml:"from"`
+	Host               string `yaml:"host"`
+	Port               string `yaml:"port"`
+	Username           string `yaml:"username"`
+	Password           string `yaml:"password"`
+	Security           string `yaml:"security"`
+	InsecureSkipVerify bool   `yaml:"insecure_skip_verify"`
+	From               string `yaml:"from"`
 }
 
 type secrets struct {