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/internal/models/auth.go

@@ -24,7 +24,7 @@ type Tokens struct {
 
 type RegistrationBeginRequest struct {
 	Username string  `json:"username" binding:"required" validate:"username"`
-	Email		 *string `json:"email" binding:"email"`
+	Email		 string `json:"email" binding:"required,email"`
 	Password string  `json:"password" binding:"required" validate:"password"`
 }