Create decorator for validation

[wovalle]

Fireorm supports validation by leveraging the responsibility to class-validator. To perform the validation we have to declare a function on each abstract repositories like (this one or this one) and checking on each function if validation should be performed with something close to:

    if (this.config.validateModels) {
      const errors = await this.validate(item);

      if (errors.length) {
        throw errors;
      }
    }

Acceptance Criteria:

• Create a Validate decorator that checks if validation should be performed and returns a ValidationError
• Create unit tests
• Replace the existing validation code with the decorator
• Each function that needs to be validated should only use the validation decorator