feat: implemented smtp service;

feat: implemented registration emails;
fix: config variables for password length used the same env variable;
refactor: all available config variables added to docker-compose.yml

backend/cmd/main.go

@@ -33,6 +33,7 @@ import (
 	"context"
 	"fmt"
 	"net/http"
+	"strconv"
 	"time"
 
 	"github.com/gin-gonic/gin"
@@ -79,7 +80,7 @@ func main() {
 
 			// Gin
 			server := &http.Server{
-				Addr:    fmt.Sprintf(":%s", config.GetConfig().Port),
+				Addr:    fmt.Sprintf(":%s", strconv.Itoa(int(config.GetConfig().Port))),
 				Handler: router,
 			}