feat: initialized smtp service;

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

backend/internal/services/smtp.go

@@ -16,3 +16,22 @@
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 package services
+
+import "go.uber.org/zap"
+
+type SmtpService interface {
+	SendEmail(to string, content string)
+}
+
+type smtpServiceImpl struct {
+	log *zap.Logger
+}
+
+func NewSmtpService(_log *zap.Logger) SmtpService {
+	return &smtpServiceImpl{log: _log}
+}
+
+func (s *smtpServiceImpl) SendEmail(to string, content string) {
+	panic("unimplemented")
+}
+