fix: wrong code in Service Autoscaling

[palateo93]

The service autoscaling does not use self.fargate_load_balanced_service which is required.

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Description of changes:
If you just uncomment the code below the comment "Enable Service Autoscaling" it does not work throwing the following error:

Traceback (most recent call last):
  File "/home/ec2-user/environment/ecsdemo-frontend/cdk/app.py", line 349, in <module>
    FrontendService(app, stack_name, env=_env)
  File "/home/ec2-user/.local/lib/python3.9/site-packages/jsii/_runtime.py", line 118, in __call__
    inst = super(JSIIMeta, cast(JSIIMeta, cls)).__call__(*args, **kwargs)
  File "/home/ec2-user/environment/ecsdemo-frontend/cdk/app.py", line 94, in __init__
    self.autoscale = fargate_load_balanced_service.service.auto_scale_task_count(
NameError: name 'fargate_load_balanced_service' is not defined

This is because it does not point to self.fargate_load_balanced_service.service.auto_scale_task_count

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