text: Title: Async email support
  Body: Currently, all emails are sent in the `mixins.py` but would be great to have async support.
  
  I think the easiest way to make an optional plug and play support would be creating a new setting to enter a function that wraps each send email call.
  
  **Actually it's not an async email support, but make easy to integrate with your own async solution.**
  
  ```python
  # settings
  EMAIL_ASYNC_TASK = None
  ```
  
   Then it accepts a function path"
  
  ```python
  EMAIL_ASYNC_TASK: "path/to/task"
  ```
  
  The task need to accept the email send function and its arguments, usage with celery would be something like this:
  
  ```python
  from celery import task
   
  @task
  def graphql_auth_async_email(func, *args):
      """
      Task to send an e-mail for the graphql_auth package
      """
   
      return func(*args)
  ```
  
  Then, in the `mixins.py`, we need to change all send email calls, for example:
  
  ```python
  # from
  user.status.send_activation_email(info)
  
  # to
  if app_settings.EMAIL_ASYNC_TASK:
      app_settings.EMAIL_ASYNC_TASK(user.status.send_activation_email, info)
  else:
      user.status.send_activation_email(info)
  ```
  
  Of course, to make this work we must import the function from its path in the `settings.py`, probably using:
  
  ```python
  from django.utils.module_loading import import_string
  ```
  
  
  
  
  
  