feat: initialized smtp service;

refactor: config now returns a copy of a struct to prevent editing;
chore: corrected identation

backend/internal/errors/smtp.go

@@ -0,0 +1,10 @@
+package errors
+
+import (
+	"errors"
+)
+
+var (
+	ErrSmtpDisabled = errors.New("Smtp is not enabled in the config")
+	ErrSmtpSendFailure = errors.New("Failed to send email")
+)